Yea, I think you have this one backward? it's lack of regulation that allows Mastercard and Visa to say "if you do try to use some other payment process you can't use us". Since MC and Visa own all of it, no business can take that hit to their customer base
Some other countries don't have this issue for various reasons.
Is it a US thing? In many countries there are definitely different payment systems accepted by merchants, just not card based and/or directly linked to a bank account.