I work in the payments industry and can provide some insight. Credit card processor HATE processing payments for porn because tons of people claim them as fraudulent. Eg: A guy spends $100 on OnlyFans and his wife sees the credit card statement and asks what it is, and he is just like "uh..... um.... my credit card must have been stolen!!"
Or alternatively somebody spends $1000 on some OnlyFans model, gets a nude picture or something, then regrets it and disputes it with the payment processor and claims it was fraudulent. Fraud claims cost everybody in the whole payment chain a lot of money.
There are alternative payment processors that will take these sorts of payments, but they charge a LOT more. A typical payment processor charges around 3%. These can charge 15-20% because they lose so much money from fraud. When your ENTIRE revenue is porn (OnlyFans), this is necessary. When you have other non-porn income (Patreon) you have to decide if that sort of fee increase is worth it. These services also do not offer their services to small companies or individuals so a single developer could not choose this option anyway.
Patreon (the company) really does not care if you game has porn or whatever. They will leave it up until the banks complain. And there is no avoiding the banks. Even if the developer quit Patreon and set up their own website. They would need to use a service to process payments. Their options are basically Stripe, Paypal, Braintree, or maayyybbe Square. Guess what? All 4 of those companies are backed by the same banks with the same rules. (Patreon themselves use Paypal and Stripe.)