I had thought the same, until I actually played it, and then it made complete sense. It's hard to express how difficult it would have been to have designed a non-VR counterpart with it until you're in the game experiencing it -- the pacing, the environments, the Combine, etc. I feel it's completely different than any Half-Life game, or FPS game that I've played, but familiar at the same time.

As far why they did a VR game at all: I suppose they like to test the waters.