Somewhere along the lines companies were given a right to be moral police about what happens on their platforms, this is the same reason ad agencies can't put ads on pirate sites, because paypal will stop paying them. Paypal also holds all your money for up to 120 days to make sure it's yours they claim, I believe it's to collect interest, but what do I know. Visa and Mastercard are allowed to say where you can use their cards and what for, if they wanted to they could stop you from buying porn with them. Unfortunately at some point companies really do become too big and when they do the morality of whoever runs them rules supreme over any kind of law.

Which brings me to that pesky constitution and why this doesn't really violate the first amendment, the constitution is quite clear that only the government can't infringe on your rights not private companies.