Correct transaction coding is required, sure, but I think you buried the lede a little. Processing transactions for adult content is very high risk because of the increased rate of chargebacks (from fraud) and the exposure to illegal activity (csam, trafficking). Stripe, PayPal etc. are very protective over their standing with card providers and regulators. Stripe could charge more to process these transactions (even enough to cover the increase in chargebacks) but the risk of processing illegal transactions isn’t worth it at any price.