Payment processors like Stripe rely on creator platforms like Patreon and BMaC for non-trivial portions of their business. That kind of demand is
why Stripe Marketplace exists in the first place. If consumers aren't putting pressure on every step of the chain, that pressure won't work its way up to the payment processors.
In other words, if marketplaces themselves aren't going to Stripe and complaining, Stripe will not fix its Marketplace TOS. A really good way to create that demand is to hold businesses that build on top of these processors accountable.
If I build a calendar app on top of Facebook, and Facebook requires me to share all of my user data with them, you can make a reasonable argument that this is all Facebook's fault for having bad terms. But even so, if my users start asking me why all of their data is going to Facebook, that puts a lot of pressure on me to look for other platforms that have better terms, or complain to Facebook that their offering isn't good enough for me.
I'm not saying that Buy Me A Coffee should be abandoned or that I want it to fail. We don't want to block better platforms or decrease competition in the pursuit of perfection.
But even if on net Buy Me A Coffee is a good service, and even if we ultimately want it to succeed, and even if the owners genuinely can't do anything at all, it is still a good thing to force the owners to go through additional friction and to endure additional criticism because of their content decisions -- because if a better, more permissive payment processor ever pops up in the future, owners that have gone through that friction will be able to see a real business case for switching and revising their policies. When Stripe advertises its Marketplace services, platforms like Buy Me A Coffee will have an incentive to say, "yeah, but my users are still going to chew me out over your policies. How can you help me with that?"
Criticism of creator platforms over payment methods creates demand for better payment methods.