Absolutely, because not all disabilities are permanent. They can broken into lifelong disabilities, acquired, temporary, situational, and chronic (potentially among others). Just think of how many people who can hear still use captioning on their TVs. Or how easy your website is to reading on a phone during a bright, sunny day. Or how usable your stuff is for someone holding a child in one arm. Accessibility (and thus, WCAG’s success criteria) helps everyone.
I don’t think it’s unusual that creators who have thought about accessibility have also thought a lot about UX, etc. So there may be some correlation there. But as others have posted, while there are some criteria more targeted at those using assistive technology (like screen readers), there are just as many things helping everyone else.
Besides all that, none of us are getting younger, and with age comes reduced mobility, dexterity, sight, hearing, etc. You never know what tomorrow brings. Someone who self-identifies as having no disabilities today may have a different experience tomorrow.
But then again, web accessibility is what I do for a living, so of course I’m a bit biased. :)
