Oculus has done extremely impressive hardware and software for VR and created the only viable mass market headset in the world and most importantly managed to ship consistently.

If he wanted to work on that there isn't really another company that he could have worked at. Valve doesn't take it seriously enough, and personally I believe they would have actually abandoned it already if Oculus hadn't been competing with them, they just lack the ambition and making hardware successful is infinitely more work than just running a videogame store.