Outside of US there are lots of payment processors that do not touch Visa/MC rails. And in US one can use ACH/Zelle. Nothing stops a business from avoiding Visa/MC. But that may reduce their customer pool, due to increased checkout friction.
"Nothing stops this, except this things that stops it."
Cause I don't think there is any kind of way to buy things with Zelle and possibly it would be a TOS issue.