People think this is about morality, but it's a lot more about the cost of operating in that market. I bet that there are way more claims of fraud, money laundering investigations, subpoenas and other overhead that the banks don't want to deal with.
Like teenagers stealing credit cards to pay camgirls is probably pretty common. And there are likely a lot of prostitution investigations.
The real problem is that sex work isn't treated like normal work, which just creates freedom for criminals to take advantage of vulnerable people.
If it was licensed and regulated, then it would be easier to tell the crooks, and victims of human trafficking from the people who are legitimate, voluntary workers.
Then the economics might make sense for banks to keep serving these customers.
