Did they tho? Steam was absolutely terrible in the beginning, the only reason people used it back in the early days is because you needed it for super popular valve games. It had nothing to do with them being a solid storefront or anything of sorts.
I have used it since a few days after release (Sept 13, 2003) because I was playing Counterstrike. It made updates and finding play servers so easy even though it did have a rough start with connectivity. Honestly, it was better than whatever we had to use prior even with the issues.
Once they sorted out the server issues and started adding non-valve games it became even more useful and we end up where we are now.
They are currently still on top because of being a solid storefront and the other things I listed.
And then look what happened after steam of companies saying PC is dead and not wanting to invest in it. It’s not like the market wasn’t open for anyone to enter. All the other companies didn’t care including Microsoft in their own platform. Even look at how barebones the launchers are compared to Steam and how all the companies didn’t care about Linux.
It’s not like these opportunities were never around and Steam just happened to get good will. Companies still are putting in the bare minimum and have more trouble or maybe disinterest in matching the features of Steam than a new company making a smartphone. How ridiculous is that. That companies making a smartphone did a better job of trying to be modern than a companies attempt at a launcher.