OK, just to qualify that statement, Steam's Wikipedia article says they had about 132M monthly active users as of 2021, and as noted in recent news, their servers can serve about 40+M of those simultaneously.Steam reportedly has close to 80% market share in the game launcher market. Epic is struggling with about 8% and GOG doesn't seem to have any percentage worth mentioning. Most people who play games will by default go to steam.
However, the worldwide market of PC gamers - of all types - is about 1.8 billion, according to Statista.
That means Steam serves just 7.3% of the entire PC gaming market.
So the notion that "most people who play [PC] games will by default go to Steam" seems a little unfounded.
As someone who used to work in the games retail sector (back when we had more physical computer games stores), all kinds of people play all different kinds of games.
We got as much, if not more profit from people who dove into the $4.99 CD-ROM bin to buy 10-15 old games at once as a "bargain," than a single copy of the latest AAA game.
I mean, it might feel galling to think about, but... I'm pretty sure both Apple and Google make a ton of profit from silly $2.99 games intended to amuse toddlers while their parents are busy. Parents will easily buy 5-10 of those if not more.
Same thing with any number of puzzle games that people buy to play in the morning or on the bus to work, or "pocket" versions of their favorite console games or RPGs, etc.
The price barrier is so low it doesn't feel like a big decision, and it doesn't require cutting-edge hardware.