Valve only came up with Steam Boxes (and it's whole Linux push for that matter) as a defensive response to the Windows Store and the, at the time very real-seeming, possibility that Windows would become an entirely walled-garden they'd be beholden to. They put much effort into Steam Boxes, they were just a PC with Valve's Ubuntu derivative distro. Fortunately for Linux users though they did continue to put a lot of effort into making Linux gaming actually viable, thus insuring that they'll always have an out if Microsoft goes stupid.