Do some people here not understand the legit reason steam is so popular? Its because of decades of good will and user focused instead of publisher focused (like epic).. It has actual user reviews, that it encourages you to do. It has per game forums, and discussions, community hubs, and workshop for mods, guides sections, etc.... All that is missing in every other launcher besides steam (gog has the forums, guides and reviews too, but it's galaxy software has issues).
PC gamers trust valve and steam. They don't trust big pubs, like ea or ubisoft, or MS, and for good reason, all those companies delist games, they take down servers and stores, and don't give options. Steam eared trust, gamers know that once they bought the game its there.
Also most pc gamers don't want seperate launchers, they like steam and want everything to come through that. Publishers may not like it but if they want good sales, then thats the way to go.
That being said, an in game overlay is great! A seperate launcher like origins or ubisoft connect, epic, etc...hell no!