I've worked specifically on payment connected to porn. Money laundering is a fact, but this being the motivation for banks to pull away is not.

There have been several scandals related to payment processing and money laundering, and some of them connected to companies that do a lot of business with porn. Usually, you will see banks breaking away when those scandals break to the public.

However, banks do not break away just because they don't like the transactions they're seeing. What they actually do is to enforce stricter rules by financially penalizing those who make them lose money. Your transactions are getting canceled a lot (by having to be flagged/undone/paid back etc.)? You'll have to pay higher fees, and if it keeps happening, you will lose your license.

You know when they do often break immediately, however? When there are campaigns by special interests groups, usually connected to conservative groups, to paint companies as having illegal content, even when they don't have this problem any more than any social media platform. In those cases, they don't wait for any tribunal.