The first real money I ever made from game development was on Android. It was in 2013, when Android was still the underdog compared to the iPhone, and was being touted as a great platform for developers.
Disclaimer:
Even though the title says "my", this is not my blogpost.
That said, it is not really beneficial for most companies to compete with Google Play since they know the user base will be smaller, user experience will be worse (install warnings, no auto-update), and people may get affected by malware if they don't pay attention to where they are downloading things from (may download a scam app directly instead of the legit app store).
I'm still shocked that steam isn't even present. They probably could manage to add it. Maybe arm versions for windows and Linux too. Maybe some magic to make it work with Linux natives? Just saying