Honestly, 99% of that is just bitterness.
I can’t say anything about the dudes who say that shit online, since I don’t know their lives (just in case anyone reading this might get all butthurt).
But, in real life, every single guy I’ve ever known who has said that, and I mean every single one without exception, the real problem was that they were hypersensitive to rejection and so never actually tried to take things in a romantic direction with women (if they ever actually interacted with women in the first place).
You talk to them, trying to figure out where they’re coming from, and they’ll have two or three stories about women who rejected them and how affected they were by it. And that’s it, that’s their life story. Meanwhile, they don’t realize that the “assholes” who supposedly have so much romantic success are out there getting rejected by more women than that in an average week.
If a dude has a problem with our culture putting such an emphasis on men making the first move, I’m sympathetic to that. If a dude is socially awkward and thus finds it difficult to navigate the dating world, I’m sympathetic to that. If a dude is so lacking in self-awareness as to not recognize his own contribution to the problem, and so egotistical as to decide that the issue must be with everyone else, well then I’m all out of sympathy.