Payment processors view this as a risk/reward scenario. NSFW content historically has very high chargeback rates. When your overall processing amount is low, the risk is low. As the amount goes up and your business gets more successful, the risk increases as your new customers are more likely to be fickle.

This is a few years out of date but when I investigated what it would take to legally accept credit cards for NSFW content, the processors all wanted a very large bond to hold as protection against chargebacks. I imagine once your daily transaction volume grossly exceeds reasonable bond levels, the processors get pretty flighty.

IIRC there's basically one payment processor, whose name I can't recall, that ~100% of NSFW sites use. And their fees are very high, given the risk of processing those payments.

CCBill is the primary one and they charge nearly 4% per transaction and routinely hold transactions for up to 6 months sometimes. They also have high registration fees but they are one of the best for high risk industries.

CCBill and Probiller or something.

CCBill's fees I think are like 11-15% plus $1k per year, pretty insane but underscores the risk

Woah, back when I was forced to implement them they only charged 4%.

They have a 3.9% ("green") tier without a high-risk fee, but I don't think the adult companies qualify that one.

I could be wrong, but I didn't find a clear breakdown of who qualifies for each plan on their website. I'm guessing the 3.9% plan and their non-profit plan are there so they can present as a normal payment processor.