Perhaps Microsoft see the direction that Valve is taking as a problem?
Valve are not the only games publisher for PCs. I can see no logical reason to restrict myself to a console that plays games from only one publisher when an equivalent PC will play those and loads of other games. (And it can be used as a general purpose computer.) If the Steam consoles were going to be appreicably cheaper than a PC then there might be a reason, but the opposite looks to be the case - pay more for a console that does less than a PC.