Ehhhh. There is a little more nuance to "thing that caused harm to you" - if my grocery store decides to stop selling some company's granola bar due to poor sales, they're probably not obligated to continue stocking it even if discontinuing it would cause harm to the granola bar producer. I would imagine there's something in Valve's terms that doesn't obligate them to be a dev's retailer any more than that developer is required to let Valve sell their product. And there is probably some clause in the contract between Valve and the payment processors.

As for the devs going against the payment processors... I have a hard time seeing a legal avenue there. It's harder when there's no direct relationship between the devs and payment processors and each party was likely exercising their rights under their individual agreements.

My bigger point is that suing for going against the desires of the users isn't really a thing while trying not to get too deep into the weeds.