Even if they managed to have a smooth store experience that was basically just buying games with a shopping cart and having a friends list… steam has a mind boggling amount of features that they would need to catch up on.
The steam community, big picture mode, controller support, family sharing, community market, the workshop, screenshot and video features, adding non steam games, I mean there are so many features it’s really hard to keep track of them.
The best crazy example I can give is that I can add dolphin emulator as a non steam game and run Mario kart double dash, then use steam to invite literally anyone with steam and a controller to my session and we can play double dash online coop that easy. Sure there are other ways to do that, but I can do this with any game ever using steam. Oh the game only supports a certain type of controller? I can remap everything using steam.
It’s way more than just a store at this point.