The quality of games on Google Play is much worse than what is available on Steam and the variety of titles are much greater on Valve's platform too, with far less in the way of microtransactions and other exploitative behaviours (though Steam isn't free of this) and a back catalogue stretching as far back to the mid 2000s.

Both Microsoft and Sony AAA titles, most third parties publish there and most indie games release there first. Steam's library is unparalleled in the industry, the only thing it's truly missing is Nintendo's games.