I think to fully flesh out this question, it would need its own topic. In brief, traditionally it’s been held that bhikkhus are required for the ordination of bhikkhunīs, per the written texts (though I am personally interested in examining the possibility of bhikkhunī-only ordination).
You might find a discussion in these two topics more fruitful:
Links
Autonomy of the Bhikkhūnī Sangha-Aj. Hiriko
“Separate but Equal”, the ideal doctrine for Monastics?
But what Ven. @vimalanyani points out is that it’s even more than just about ordination—it’s about recognition and equal status. In an ideal world, it wouldn’t matter what the men think. But in the world we have now, often Buddhists look to the bhikkhus for guidance and direction, and when they see indifference, disrespect, or downright hostility towards women—then consciously and unconsciously it sends the message that that’s the proper way of things.