Law enforcement does enforce laws for things like this, one of those ways is through finances. Risk averse and perhaps morally motivated, payment processors see a poorly regulated market and choose not to participate in it.

Pornography is hard, it's on the interface of liberty where if you want to maximize freedom, it isn't just a simple action. You need to be careful to protect people in their freedom to express themselves, and you need to protect people from being abused.

>these seemingly arbitrary decisions can be extremely impactful

One would hope that they are impactful. An enormously profitable industry has not been doing enough to protect people from the abuses the business encourages and is thus threatened with losing the ability to sell its product. I really don't see a problem with that.