Because softcore anime/manga-style is both a very specific niche and one which is at least partially covered by a dozen faster boards.
Also you have to post 6 images to start a theme request thread, which is a higher bar than most of those other boards.>>2562757
/a/, /jp/, /vt/, /v/, every /v/ split, etc. are evidence to the contrary. But there are a lot of anons who don't care much if nipples and genitalia are covered if they're fapping to an erotic drawing of an anime girl.