But Steam doesn’t have a monopoly. There’s Epic and GOG and whatever Origin’s called now and probably others. They’re all free to exist, Valve doesn’t do anything to stifle competition, and even lets other companies sell games that start their launcher from Steam.
The only thing you have to lose by using a different system is that it’s probably not as good.
All they’ve done is produce a really fucking exemplary product and it’s become really popular because it’s honestly just good. The second it stops being good or Valve stop being awesome there’s plenty of alternative ways to buy games that I’m sure will be there to replace it.