I doubt anyone is threatening banks on this based on moral grounds.

I suspect it's just fraud, people using stolen credit cards and bank details to pay for porn (because porn can be delivered digitally)

So these accounts disproportionately show up in the fraud department and the fraud department spends more time dealing with those accounts than the profit generated.

Eventually, the bank or payment processor decides it would be less effort just to get rid of the customers causing issues. The moral questions probably means nobody internally feels like defending them.