What steam brought to the table was the first content delivery network for games. Digital Marketplaces were not a thing when Steam launched, and most software was still sold on store shelves. They are reliable, and customer friendly - that’s why no other content delivery network has gotten any kind of foothold, because competitors consistently create platforms that are more difficult to navigate and screw customers over shortly after their launch by removing content or having some sort of major rights-issue.
Steam Workshop and Steam Community market account for almost nothing in the grand scheme of what makes Valve its money.
They have spent tons on developing the tools to play games on Linux through Proton, and have shown themselves to be enthusiasts themselves when it comes to supporting gamers with some of the more robust VR systems as well.
Its content delivery network for games existed without those things 15 years ago is my point. If the argument is that being privately run exempts them from the need for constant pointless expansion, there is no greater contradiction of that than examples where it expanded pointlessly. Systems which they hired an in-house economist to develop; whom rejects their modern implementations on the principles I described.
Also, GOG exists.