Why do you think animation isn't mainstream adult content in the US?
Or maybe it's better to ask why animation is mainstream adult content in Japan and more of a subculture around the world? Just watched Fullmetal Alchemist and it really got me wondering why outside of Japan tv animation for adults never gained popularity. Does anyone here know the answer?
It's seen as immature I would think. Also eroticized to an extent
It’s cultural. Japan animation content is extreme, either in gore or the opposite of it. We are not accustomed to watching children in adult context while Japan has been comfortable with it to put it the mildest way. The good ones that fit America more are still popular here. For example, one punch man. The ones with kids giggling and mutter kawaii are obviously not.
Japanese animation also tends to feminize men. Not all, but just the illustration style is more soft. I’m Asian, and watched anime growing up. Now that I’m older, I feel like there is a pressure to not watch it anymore because society deems it childish. Also, America tends to still prefer the “macho man” vibe. They don’t like effeminate men who have long silky hair and a lanky build as the hero. It also has to do with society and dating and what people prefer. Check out the herbivore man in Japan. This just further separates our two cultures.
I think your entire premise is off. Is Japanese anime accepted as mainstream adult content in the US? No, not really. But is animation accepted - definitely! Archer has won multiple Emmys, there’s Venture Brothers, Rick and Morty, Boondocks, Afro Samurai, Futurama, Seth McFarlane’s multiple shows, hell the entire Adult Swim franchise has been serving up adult animation for two decades. Just expand your focus beyond anime (nothing against it, I love anime but it’s not seen as mainstream for adults) and you’ll see a thriving adult animation industry.
There are some! For example, South Park and Family Guy. The reason might be there are lack of good works in here.