Origin, Blizzard, uPlay et al failed to challenge Steam largely because they lack both features and catalog; it's not clear they even intended to take on Steam, because of the lack of content from other publishers.

EGS is worth special attention because it both has content from other publishers and has dumped considerable cash into the goal of unseating Steam. I think it comes down to features: the EGS store has generally been a sub-par experience, and they purposefully refused to implement features like Community Scores, Forums, and other metasocial features that make Steam what it is.

They underestimate the value of player reviews, community scoring, forums, guides, workshop and so on. Even if most of users of most games don't avail themselves of those features, they're important features for retaining the most die-hard of users; who in turn form the core of the social draw to use Steam.

Because copying is theft. I kid...