It's not even about banning all porn, it's about banning porn that is funded through a public platform like Patreon. Paypal and Visa don't care if you use them to buy brazzers subscriptions because brazzers is doing their own thing with their own investors' money. Hell you could be buying sex slaves through a third party and as long as the transaction itself was bona fide they wouldn't give a shit. It's how finance capital works, if you've got it you can do with it as you see fit - open a nickel-cobalt mine in the Congo ruining the environment and thousands of lives in the process or start an environment-friendly cupcake IPO in Andorra.
But look, some anonymous zoomer dweeb makes $300/month on Patreon drawing tentacle rape pron in his mom's basement! Let's target *that* guy because obviously he is a threat to women everywhere. But really, because he doesn't matter and getting rid of him ticks a PR box for the people holding the real money. It's one thing to use payments services to buy content from an established porno giant that has stocks in private exchanges, often traded in by folks who invest in Tesla. Quite another to use them to ask for donations to support your 3d porn rendering career on a publicly traded crowdfunding website.
I'm not even saying that porn is 'fine'. Clearly the industry abuses a lot of women in every sense of that word. However all of that is irrelevant for animated/rendered/voiced porn, the kind that virtually all of these patreons are creating. So why is it still a Bad Thing? Because a>these businesses operate inconveniently for the businesses that matter (and their partners/customers) b>the market itself is way too small in the grand scheme of things to be standardised, invested in, validated, glamourised and protected from scrutiny.