Honestly, even if the government did attempt to regulate them, what's to stop MasterCard & Co from just telling them "no"? What are they going to do, shut down the credit card processors in America? The entire economy requires those to function. They've made themselves into a required part of the way the country operates on a day to day basis. If you turn off the debit and credit cards of all American citizens then 99.99% of all commerce grinds to a screeching halt instantly. Some people will have, or be able to get, cash money and make do with that in the meantime but many many more will not. I imagine crypto might become a more legitimate market in this situation, because otherwise you just straight up can't buy things online anymore. But how you obtain crypto from cash money, I could not tell you. I imagine it looks like a shady drug deal involving a USB drive.

Especially in the modern political climate I could easily see our government trying to say "you can't do that" and then Visa/MasterCard just respond "yes we can" and then yes, in fact they can, no matter what "that" is today, because any tangible threat to them will also crash the national economy.