Big porn companies are very serious about PCI compliance. They also closely monitor their fraud numbers. If a MID (merchant ID) goes above 5% (volume or cash amount) fraud, the processor could get fined by Visa/MasterCard/etc ($50k+) and lose the right to accept credit card payments for that particular payment network. Processors who handle porn (high-risk) accounts will often have a general, shared account they'll let you use, because they can take measures to average down and hide the fraud. However, they charge you a premium to use that general account, so you're better off using your own if you have other measures to control fraud.

My former company solved this problem by simply acquiring a payment processor company. They had total control over their processing that way. As a bonus, they had access to other porn vendors' account activities, since it was one of the 4-5 major high-risk processors used by porn companies. It was a win-win for them.