I received a very generic automated message that said it could have been due to "nature of content" and "risk." Attempts to reach out to Itch staff via email and through their Discord have been met with radio silence.
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At least the benefit to PC gaming is that you can pretty much dump games on multiple storefronts so if one bans it then you can try another. You should try Epic Games Store, Nutaku, MangaGamer and Denpasoft.
It's an embarrassment that even in this current age of gaming, censorship is still as rampant as ever, if not even worse than before. Censorship ruins gaming, not benefits. If possible, you should also release it for macOS and Linux.