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In the USA, some things that come to mind:

* Legal changes. Web platforms have section 230 protection to host user content. For payment processing this might be something like the proposed Credit Card Competition Act (CCCA) that requires banks to offer additional (non-Visa/Mastercard) payment providers. Or a more explicit payment neutrality law the requires credit card companies to be more even-handed in non-financial issues. Or anti-debanking laws that ensure everyone has some minimal access to sending and receiving payments.

* Lawsuit results. Part of the issue with Visa was that they got dragged into lawsuits against sites that were using them to process payments; the lawsuits and appeals around that are still unresolved but if Visa's lack of legal liability goes away then it will be harder for random outside groups to harass them, for good or ill.

* Introducing an independent payment processor. While JCB in Japan has had some similar pressure applied to them, when there were national sovereignty concerns over Visa being able to dictate that American laws and norms should apply to their country Japan had many other payment processors to fall back on. Similarly, PIX in Brazil makes it much harder for non-government private actors to dictate what people can and cannot buy.