Why Gandhari and Mandodari are glorified in Srimad Bhagavatam?

Saubalinī, or Gāndhārī, daughter of King Subala and wife of King Dhṛtarāṣṭra, was ideal as a wife devoted to her husband. The Vedic civilization especially prepares chaste and devoted wives, of whom Gāndhārī is one amongst many mentioned in history. ( Srimad Bhagavatam 1.13.30) 

Not only was mother Sītā powerful, but any woman who follows in the footsteps of mother Sītā can also become similarly powerful. There are many instances of this in the history of Vedic literature. Whenever we find a description of ideal chaste women, mother Sītā is among them. Mandodarī, the wife of Rāvaṇa, was also very chaste. Similarly, Draupadī was one of five exalted chaste women. As a man must follow great personalities like Brahmā and Nārada, a woman must follow the path of such ideal women as Sītā, Mandodarī and Draupadī. By staying chaste and faithful to her husband, a woman enriches herself with supernatural power.(SB 9.10.27 purport)

Despite their husbands Drthirastra ( Materialistic person) and Ravana (demon), sastra glorifies Gandhari and Mandodari as examples of chaste women. Even though their husbands are not devotees, yet they did not force their dharmapatni in adharma. Dhirthirastra was a materialistic person, atlast purified by the good association of Vidura. Gandhari followed him till the end of the life. So, she attained perfection and elevation. Ravana- powerful demon, he was unconquerable because of the boon from Lord Brahma. Even the demigods feared him, he was unconquerable because of the chastity of Mandodari. He was destroyed because of his kidnapping Mother Sita and her curse. Power of chastity destroyed Ravana. Both Gandhari and Mandodari tried to advise their husbands to avoid war. It is the duty of wife to advise husband in righteousness. Gandhari and Mandodari did their duty perfectly and attained elevation. Prahlada Maharaja was born to Kayadu, wife of demon, Hiranyakasipu. 

Even the demons didn't force their wives in unrighteousness and they also followed Varnasrama dharma. They were killed by the Supreme Lord because created trouble to the devotees. 

Thereafter, all the women whose husbands had fallen in the battle, headed by Mandodarī, the wife of Rāvaṇa, came out of Laṅkā. Continuously crying, they approached the dead bodies of Rāvaṇa and the other Rākṣasas. Srimad Bhagavatam (9.10.24)

Striking their breasts in affliction because their husbands had been killed by the arrows of Lakṣmaṇa, the women embraced their respective husbands and cried piteously in voices appealing to everyone. (9.10.25)

Following are the verses in Srimad Bhagavatam spoken by Mandodari, wife of Ravana : 

"O my lord, O master! You epitomized trouble for others, and therefore you were called Rāvaṇa. But now that you have been defeated, we also are defeated, for without you the state of Laṅkā has been conquered by the enemy. To whom will it go for shelter?"

Purport: 

Rāvaṇa’s wife Mandodarī and the other wives knew very well how cruel a person Rāvaṇa was. The very word “Rāvaṇa” means “one who causes crying for others.” Rāvaṇa continuously caused trouble for others, but when his sinful activities culminated in giving trouble to Sītādevī, he was killed by Lord Rāmacandra. ( 9.10.26) 

"O greatly fortunate one, you came under the influence of lusty desires, and therefore you could not understand the influence of mother Sītā. Now, because of her curse, you have been reduced to this state, having been killed by Lord Rāmacandra."

Rāvaṇa was condemned not only by Lord Rāmacandra but even by his own wife, Mandodarī. Because she was a chaste woman, she knew the power of another chaste woman, especially such a wife as mother Sītādevī. (9.10.27)

O pleasure of the Rākṣasa dynasty, because of you the state of Laṅkā and also we ourselves now have no protector. By your deeds you have made your body fit to be eaten by vultures and your soul fit to go to hell. 

Thus the destination of godless atheists such as Rāvaṇa, Hiraṇyakaśipu, Kaṁsa and Dantavakra is a hellish condition of life. Mandodarī, the wife of Rāvaṇa, could understand all this because she was a chaste woman. Although lamenting for the death of her husband, she knew what would happen to his body and soul, for although one cannot see directly with one’s material eyes, one can see with eyes of knowledge (paśyanti jñāna-cakṣuṣaḥ). In Vedic history there are many instances of how one becomes godless and is condemned by the laws of nature. (9.10.28) 

Sastra gives us examples of chaste wives in various circumstances. This should be understood carefully. Whatever may be situation, women are taught perform their duties properly. It doesn't mean everything is will be perfect. Gandhari has suffer very much, still she tolerated so she is described as tapasvini in Srimad Bhagavatam 1.9.48,

gāndhārīṁ ca tapasvinīm

Gāndhārī was a powerful ascetic, although she was living the life of a faithful wife and a kind mother. It is said that Gāndhārī also voluntarily blindfolded her eyes because of the blindness of her husband. A wife’s duty is to follow the husband cent-percent. And Gāndhārī was so true to her husband that she followed him even in his perpetual blindness. Therefore in her actions she was a great ascetic. Besides that, the shock she suffered because of the wholesale killing of her one hundred sons and her grandsons also was certainly too much for a woman. But she suffered all this just like an ascetic. Gāndhārī, although a woman, is no less than Bhīṣmadeva in character. They are both remarkable personalities in the Mahābhārata

Why did she blindfold herself? 

From Mahābhārata we learn that when Gāndhārī understood that her would-be husband, Dhṛtarāṣṭra, was blind, she immediately began to practice blindness herself. Thus she covered her eyes and played the part of a blind woman. She decided that since her husband was blind, she must also act like a blind woman, otherwise she would be proud of her eyes, and her husband would be seen as inferior.

 

Gandhari blindfolded her eyes is such an great vow. It shouldn't be imitated nor do kali yuga women have such power to do so. The essence of such instruction should be understood. 

First lesson: is to avoid pride. It's natural for any person to be proud if he is better than others. Secondly, she did not want to enjoy sight because her husband couldn't do so. She doesn't want to enjoy anything that her husband wouldn't. Same example we can observe in the ideals taught by Draupadi, 

" whatever my husband doesn't eat, whatever my husband doesn't drink, whatever my husband doesn't enjoy, I ever renounce" 

This essence we learn from ideal chaste lady Gandhari. All this Gandhari did out of her love for her husband not by force. No one told her to blindfold herself. No one told her follow her husband to forest. 

The gentle and chaste Gāndhārī, who was the daughter of King Subala of Kandahar [or Gāndhāra], followed her husband, seeing that he was going to the Himālaya Mountains, which are the delight of those who have accepted the staff of the renounced order like fighters who have accepted a good lashing from the enemy. 1.13.30

As a woman Gāndhārī could have remained at home or at her father’s house, but as a chaste and gentle lady she followed her husband without consideration. Instructions for the renounced order of life were imparted to Dhṛtarāṣṭra by Vidura, and Gāndhārī was by the side of her husband. But he did not ask her to follow him because he was at that time fully determined, like a great warrior who faces all kinds of dangers in the battlefield. He was no longer attracted to so-called wife or relatives, and he decided to start alone, but as a chaste lady Gāndhārī decided to follow her husband till the last moment.

While outside observing her husband, who will burn in the fire of mystic power along with his thatched cottage, his chaste wife will enter the fire with rapt attention. 1.13.58

Gāndhārī was an ideal chaste lady, a life companion of her husband, and therefore when she saw her husband burning in the fire of mystic yoga along with his cottage of leaves, she despaired. She left home after losing her one hundred sons, and in the forest she saw that her most beloved husband was also burning. Now she actually felt alone, and therefore she entered the fire of her husband and followed her husband to death. This entering of a chaste lady into the fire of her dead husband is called the satī rite, and the action is considered to be most perfect for a woman. In a later age, this satī rite became an obnoxious criminal affair because the ceremony was forced upon even an unwilling woman. In this fallen age it is not possible for any lady to follow the satī rite as chastely as it was done by Gāndhārī and others in past ages. A chaste wife like Gāndhārī would feel the separation of her husband to be more burning than actual fire. Such a lady can observe the satī rite voluntarily, and there is no criminal force by anyone. When the rite became a formality only and force was applied upon a lady to follow the principle, actually it became criminal, and therefore the ceremony was to be stopped by state law. This prophecy of Nārada Muni to Mahārāja Yudhiṣṭhira forbade him to go to his widowed aunt.