Part of the "nice guy" phenomena is that they've been bought up since an early age to view sex in a moralistic manner. That if you've respected women, if you bent over backwards for them, if you were sensitive and accommodating etc, they'd truly value you and would opt to date you. But obviously we see the opposite where women opt to sleep with Chads, alphas, badboys etc, with physical attractiveness being favoured whilst abrasive attitudes were overlooked.

From an outside perspective, it seems like women only go for "assholes" when in reality they just happen to be attractive, assertive men. Female sexuality can be viewed as such an enigma which can make one angry, confused and frustrated if they're unable to attract. Evolutionary psychology may not be absolute and empirical at all times though it does provide an plausible explanation on human behaviour.

Certain impulses and instincts can often be independent to what society usually teaches. Most of the anger stems from not necessarily the pragmatic nature of people but rather feeling like you've been "lied to" and "robbed" of your masculine potential. The people formally at /r/incels were a different open can of worms to begin with since the majority of them had a toxic upbringing of being abused/bullied so they're naturally angry at the world for those reasons rather than just female sexuality alone.