As plenty of people have gone into the production pipeline, I'm gonna comment on the history of anime and manga and how that affects the way they're produced, since I did a paper on it many years ago.

Manga dates back at least to the era of woodblock printing, as a famous artist by the name of Hokusai released a collection of prints titled The Manga, but the manga we know today was actually originally inspired by serialized Sunday comic strips from American newspapers imported via South Korea. The comparison to modern Western comics is clear, but I think this connection to the Sunday comics is why production houses like Shonen Jump have their weekly releases which allows them to try out new artists and comics without as much risk as Western comic publishers would have starting a new series with a full comic debut. Manga books can be better thought of as anthologies of weekly comic strips like Calvin and Hobbes rather than superhero comics.

Anime is very much inspired by Disney films, but both anime and manga target demographics of all kinds and every genre you can think of. I think this goes back to the woodblock prints of yore, which were an artform that had no particular demographic or subject matter, ranging from raunchy porn to advertising for theatre shows and anything in between. Add in the economic boom that Japan went through in the 80s just as anime was taking off - a time where money was so easy to come by in the industry that they were just greenlighting pretty much any project regardless of subject matter - and anime had no qualms about portraying adult themes like sex or body horror, as well as deeper musings like the common references to the atomic bombs and the deep cultural trauma that did to Japan.

Also of note: America was actually one of the last places to be introduced to anime and manga, and it took a long time to take off here. The rest of the world was getting into anime during the 80s while Steven Spielberg is quoted as saying that a cartoon movie for adults would never take off in the US in reference to the theatrical release of Akira, the profits of which funded many of the most famous studios of the 2000s.

In short, the cultural gulf between America and Japan divested the newspaper comic strip of its stereotype as a media for kids, which resulted in an artform that catered to all audiences and interests. And upon circling back to America decades later, this lack of the stereotype and willingness to show deeper stories found a niche that had been completely unattended to amongst the teens of the 2000s, who gobbled up media in a form that they had grown up with but treated with more respect than most kids' cartoons. Also, it probably helped that many kids' shows were created with the sole intent of selling more action figures.