VR is not quite at a point where making such a bold release can be considered "better" than PC gaming or even console gaming. Using your body(+handset) in VR is still more awkward than using a controller, even for FPS games.
On top of all that is the dealbreaker... the amount of games that are directly supported for Valve Index controllers is shockingly low. Even for a newly released hardware, the number simply isn't good enough.
I've had the Valve Index for almost half a year now. Sure, it works great and it seems like a step into the future.. but neither the industry nor the market is there yet. It seems like Valve it trying to kickstart the market with a release of the most anticipated game in history.. and I somewhat doubt that it was the right move to make it an exclusive.
..because the point is, even if VR would eventually take over from PC gaming, it won't happen with a single game. Not even if it's the best game that's ever made. For 30 years several generations have, not only grown up with, but been completely shaped by PC gaming. Maybe they are investing in a new generation? Who knows.