Earlier quoted context omitted.
What is stopping MasterCard and Visa from banning Coinbase and others if this happens
They can't ban everything, since at the extremis you could buy crypto from eBay sellers. But in the long run you are right: to avoid MasterCard and Visa we should move everything to crypto. It is the only way to control our own destiny.
This is against eBay's policies. All items sold through their site must be delivered physically. If you type "bitcoin" in today you'll only get hardware or novelties, not the coins themselves.