The payment processors don't object to you. They usually object to the store or the platform you're getting things from.

It's invisible, insidious censorship. They don't hit your hands with a ruler and say "stop, no buying that, bad". They make it so that what they don't like doesn't get to be on the store shelves in the first place. Hard to buy what isn't being sold, isn't it?

As for why they do it - it's unclear, but there's speculation that payment processor leadership might be in part ideologically captured by the usual "think of the children" moralizers and puritans. The same types that used to spurn moral panics, rally against D&D and later GTA, and are the first in line to propose sacrificing freedoms for imaginary safety - now allowed to wield covert influence over most of the payments that happen online.