This is the brilliant fact underlying nearly all accessibility work: in addition to the people with documented permanent disabilities that are the official beneficiaries of such developments (and regulations where those exist), there are hosts of people who are temporarily disabled, who are disabled but undiagnosed, who are not quite over the margin of "disabled" but who are less able than others, who have temporary needs that aren't disabilities at all but just benefit from different routes to access, or even who just plain have different preferences. The ADA in the US is a great example of this—a lot of the stuff it mandates makes your life better even if you're just, say, pushing a stroller and don't "need" the ADA-mandated ramp.

So yeah, best practices for disability accommodation are not just about handling the "<1%" (as someone in a different thread put it) that need them.

The argument "it's good for SEO!" sometimes helps convince colleagues/customers who are otherwise unconvinced. Well, whatever floats your boat..