I think it's just priorities, those other companies weren't interested in making a launcher, they were interested in tying their customers into their eco system.

Steam started out like that in appearance at least, nobody really wanted it and it was kind of forced on you if you wanted to play HL2 but since Valve seemed to understand the value in a platform like steam and actually work at making it good it became pretty good.

At this point it's actually kind of hard to fully appreciate how much work has gone into steam. Not just the basic stuff like chat and forums and a store with a functioning search, or the banal stuff like inventories and trading cards and points I still don't understand, but also the stuff most people don't see like all the stuff for developers launching a game on steam and managing sales and keys and betas. Not to mention all the experiments they've done along the way to try and figure out what the best way forward is.

Steam is kind of a huge undertaking and unless a company is really invested in competing with it they're simply not going to be able to.