"O, see how fortunate are these demigoddesses, the wives of the demigods." Vanitotsava means that the demigoddesses were seeing this rasa, hearing the flute-song of Krishna, and seeing His beauty. Although they were in the laps of their husbands, in their puspa-vimana, flower-airplanes, they fainted. They forgot everything: "Where am I? What am I doing? Who am I?"
There is something here to note. Can demigoddesses see rasa-lila? They can, but their husbands cannot. They are compared with the yajna-patnis, the wives of the brahmanas of Mathura. The yajna-patnis came to Krishna and pleased Him with very sweet preparations, but their husbands were very far away. Similarly, the demigods were there, but what did they see? Nothing. They were hearing something, but not seeing all these mahotsava's, festivals, like rasa-lila and others. Their wives were seeing, however. They were taking darsana.
The hearts of males are very hard - very hard. They will be very hard to melt. But the demigoddesses' hearts melted, and so they wished that, "We should serve the gopis." They can wish.
Srila Bhaktivedanta Narayana Gosvami Maharaja: Murwillumbah, Australia, January 21, 2001