Even if not all anime are this perverted, but for every Jojo or Saitama there’s going to be yet another super-cliched or sexualised anime that’s only appealing to a certain demographic. When coupled with that Japan’s got a rapidly ageing, xenophobic population and far fewer barriers of entry to outsiders aggravates things.
Japan might be improving itself though it’s a matter of time when it’ll reverse such issues or not. If not, some other country would succeed it in adult animation. Not that there won’t be anymore smut but smut has its time and place and it needn’t to always dominate characters and plot.
It could easily be redundant. While one might argue that characterisation can counteract those, not when the characters themselves are stereotypes. But it could be that some anime fans get mad if somebody criticises their love of porn. Don’t be too surprised if an anime veteran criticises the industry for being too sexualised.
It’s been there and knows it’s neither fun nor glamourous. Just ask how Shelley Lubben or Pamela Anderson feel about working in porn.