they can do 30/50% less fees than incumbent visa/MC and still operate in the ecosystem because all local gateways and tech stack has been built to incorporate Rupay card system same as visa/MC. the end result is, suppose tomorrow USA orders visa to quit india, beyond a few hiccups, there is a good chance india can weather these american companies leaving the domestic ecosystem. that way, the indirect control USA has over the financial infrastructure of entire nations is reduced to a great extent. seems russia has done the same so this is moot now but think of it this way.
visa/MC often cry to mommy USA about unfair advantage to rupay cards in india and the US tries to intervene. suppose india bans Visa tomorrow, why is the US government so inclined to intervene in that case? unless this is their way of maintaining a degree of control