I think the difference is that on a PC, the barrier to installing Epic or GOG is the same as Steam, but with phones and tablets, the operating system itself does everything it can to scare you away from installing an "unofficial" app. There have been plenty of bad actors on the Play Store, but Google is fine pretending like their store is perfect and secure. The fact is, we live in a world where most people take the path of least resistance, and Google is using their money and power to incentivize manufacturers and end-users into certain behaviors. That just harms smaller companies from being able to properly compete.