Valve is swimming in money and Gabe Newell is set for life with his Microsoft money. Projects get started by groups of employees coming to him saying they want to work on this or that. TONS of Valve projects have been started or explored that don't lead to making any money at all, like making a tongue controlled input device ect. I think it all gets started because Gabe just thinks it's cool and is willing to budget for it.
Finding out how things "work" in VR is really uncharted territory. This game was approved and a lot of time was spent on it despite it making no business sense because the number of those with VR hardware is insanely small. It's just because Gabe and the developers think it's cool and want to be the first to make the legit first AAA VR game.
Someone is already working on a mod to make the game non-VR, Valve know it and they don't even care.