JSX makes it impossible to crap out invalid HTML because it is a library + toolchain (+ entire ecosystem) that keeps it from happening. JSX is always checked for validity before it gets close to the user, so the most irritating failure case of XHTML just doesn't happen.

XHTML never had they benefit. My point is that if libraries like React or Vue had been popular at the time of XHTML, then XHTML's strictness wouldn't have been an issue because JSX always generated valid outputs (well ignoring compiler bugs which I far too damn many of early on in React's life)