>>11326202 (OP)For the same reason everything goes to shit: normies.
Back in the day hentai was "that weird cartoon porn that only creepy weirdos watch". Hentai (and to a lesser extent all anime) was a niche that no one talked about, if you knew you knew.
Then anime became popular, and by extension hentai become popular. During all this time the world was progressively becoming more and more blatantly open about sex, gays, gender, yadda yadda, and it became more appropriate to openly talk about sexy stuff in public. It was really only a matter of time until the same people who once hated Hentai (and anime, and D&D, and WH40K, and Crypto, and just about everything else that was once niche) completely changed their minds and decided they actually love it, but only if and when it fits into their box. Because normies are the majority, the market for all that stuff will naturally shift to the newest cash cow: i.e. lowest common denominator. It happens to everything: something starts off with a small following, grows, and once it hits the public eye its nature drastically changes (usually for the worst, but rarely overnight) over a long period of time; like a slow and gradual decline of civilization if you wanna be autistic about it (which I do).
Don't believe me? Examples include TV, the internet, computers in general, memes, video games, crypto, AI, and of course: being gay/trans. All of these things started with a small following, became controversial for some period of time when reaching the public eye, and then out of nowhere exploded in popularity and have since become usurped by consumers who love it all of a sudden and try to enforce a new set of "rules" for how it must be presented.
Either a series dies great in obscurity, or persists long enough to watch itself become cancer.
Does that answer your autistic question?
