> I’m sorry, I don’t see the difference here between them and say, Walmart?
The number of customers who patronize only Walmart for any given class of goods, and never use Amazon, Target, Costco, Dollar Tree, etc. is negligible. If Walmart won't carry your stuff, you can sell to the same customers through many other stores.
The number of customers who patronize only Google Play for mobile apps is a pretty good approximation for the number of Android users. There is no plausible alternative to sell to those customers. Amazon is a serious alternative to Walmart; Aptoide is not a serious alternative to Google Play.