This whole announcement has been a damned if you do, damned if you don't scenario for Valve in terms of reception. At this point Valve has put a lot of investment in VR. For years people have asked for a big first party VR game from Valve, often explicitly a Half-Life game. They announce it and many responses are "why did Valve release a game for their own hardware". It's possible that growth will slow in VR and Valve will give up, but why do it now when they have a game ready for release and solidly selling first party hardware?