The latest steam big picture mode contains Interface->Allow access to linux desktop checkbox (tested under steam -steamos), so it does not seem they totally ignore the possibility.
Like it was sayed already.
Steam OS it is just big picture with a linux kernel behing a a few packages, just essential for gaming on it.
Big picture + auto-updates + some multimedia thing.
But essential is a operating system design to have on a TV, to be used with a gamepad.
Not to be used with kb/m and to do our daily work.
I guess most of the people didn't get it, and still dreaming of having libreoffice there and CAD applications, i laugh hard when they say that