Phone is the platform. You can put any payment system there. In various countries it was figured out in a lot of different ways. Valve with global reach could really compete.

Also Google Play store might have more consumers and or sales but they are of worse quality. It's scummy, it's exploitative. The whole system is propped up by whales decieved by gambling mechanics and deceptive ads. It's nowhere close to real world economy. Valve is much closer. Despite using Play Store since it came to existance I never paid for anything on Google Play because I don't trust it enough to add a single payment method there.