Games give a relatively straightforward "pass-fail" criteria to test out new tech. Instead of a nebulous "does this tech directly help people", it's much easier (and more objective) to say "can I get this graphics API to push N fps to make the gameplay more pleasant?". Virtually any time I learn a new programming language or toolkit, the one of the first projects I do to get my grips with it is usually a simple 2D platformer just to stress out edge cases. Is this 'useful'? Not immediately, but it is useful for me to have learned how to code well enough to make a game perform well.
It's not like these optimizations and tools can't be useful for other things after they're developed for games; Unity was primarily made for games but I have friends who use it for developing "useful" iPhone apps now.
If the technology for VR gets good enough (and cheap enough) to get into the hands of the average gamer, I cannot see how that won't be a net win for people with disabilities in the long-run.
The cheaper, more reliable, and easier-to-build VR is, the more likely you’ll see stodgy old companies (of the kind that build and go through FDA-certification for accessibility aids) becoming interested in working with it.
Sort of the same idea as Tesla: sell people a Veblen good (fancy EV cars), to fund the development of a technology (batteries) to drive the commodification of the EV industry, such that everyone non-fancy EV vehicles will become affordable, and such that EV technology will become something “obvious” to even the stodgiest auto-maker.
Or, to put that another way: you’d never have seen a direct evolution from mainframe computers to the modern PC, because the grass-roots demand for doing what a mainframe does on your desktop just wasn’t there (until it was.) The industry needed to start with calculators, evolve those chips up into microcomputers and kit them out to play games, and sell those as whiz-bang consumer electronics. Progress in that game-playing microcomputer space then carried PC technology along for the ride, until they just-so-happened to become able to do what mainframes could do.