Steam is kind of like having an Atari (the ‘first’) or the one system you own where all your games are at. Think of it that way hence the obsession of keeping everything in one place. If you look at it there's Rockstar, Uplay, Epic, Origin, Bethesda, Blizzard along with Steam and GOG. Even some phone games have their own launchers on PC. It's ridiculous.
GOG for me is probably my favorite overall but pretty much everyone started out with Steam.