I'm trying to understand under what circumstances he was working. Some of his female anatomy is EXTREMELY off -- did he not have, say, even ancient Greek and Roman sculpture to look at as a better reference for the female form?
TL;DR: It wasn't lack of models. Art is subject to its times.
Michelangelo drew and sculpted burly dudes, fat dudes, realistic women in dresses, old women is hats, snakes and subversive humanist messages relating to brains. There wasn't anything he couldn't draw. Because Michelangelo was the sort of genius that make lesser geniuses feel bad about themselves. And yes, he could draw realistic female nudes.
So, if some of his women look androgynous, it's because he wanted them to look androgynous.
Why?
Well, he was gay, but I think that's a ridiculously surface answer. A slightly better, but less satisfying answer is that all art is subject to the currents of the culture it was created in and people of the renaissance, at least people who bought art, wanted men and they often wanted androgyny. It was partly because Michelangelo (and Leonardo and Donatello) were creating such beautiful work that happened to be androgynous, but it was was sexism and homosexuality, it was a fad and it was deeply entwined with Church power structures. It was the result of a million things, but lack of ability was not among them.
People just liked dudes looking like ladies and ladies looking like dudes. It was a thing.
Just to put to bed that this was a homosexual phenomenon or the idea that artists were limited to male models only, here's a Raphael sketch. Not as buff as Michelangelo's women, but still pretty masculine.
Raphael was straight (so straight he allegedly died of too much sex with his mistress). And he did use female models in his art. Here's the woman that allegedly sexed him to death, definitely looking like a woman. Not a bad way to go, really.
As a side note, doing a search on "Michelangelo nudes" or "Raphael nudes" is fine, but doing a similar search on Leonardo or Donatello is bonkers. Don't do it with safe search off, unless you like TMNT porn. Or DiCaprio porn. Or both.
[edit: I am terrible at internet. edited a million things]
Michelangelo was most likely homosexual. I don't think he wanted to look at naked women.
