Gamers love relay servers, NAT punching, automatic updates, matchmaking, friend lists, achievements, community forums, screenshot sharing, streaming and more.
Gamers love platforms and what they provide at least as much as they love games themselves.
Those are all features a platform should provide. Nothing about those features require that the game itself becomes unavailable should your Steam account be disabled or if Steam disappears, or that the game cannot be moved to another PC based platform. Creating a platform that allowed for/encouraged that would be a serious competitor to Steam in my opinion.
Nothing? Steam provides these features in order to maintain the network effects; losing the library exclusivity would be a crushing blow to that strategy.
They'd have hundreds more of my dollars if they worked that way. GOG gets most of my money now and I get none of those, admittedly very nice, networking and social features Steam is so great at providing.
