I think it has to do with some law where banks are required to cut all financial ties to any company that aids in the production, purchase or selling of CSAM and Sexual Trafficking content etc. so many businesses are wary of any website that provides adult content unless there is the strictest of moderation and verification procedures.

Which is one of the reasons many websites (tumbler, Reddit) are limiting NSFW content because they want to be able to have users buy things on their website but don’t want to moderate the content to the standards of the banks.