Even if there was a popular alternative, there will simply be apps only on one store out of convenience. Just look at the PC market.
And most of the time PC leads to multiple releases as platforms tend to make it as easy as possible to release across multiple.
Sure the majority of games are on one but a significant fraction of the popular ones are on multiple.
Even if there was a popular alternative, there will simply be apps only on one store out of convenience. Just look at the PC market.