Recent drafts do tend to get circulated amongst the image compression community. For wide audiences I don't think this type of document is very readable nor relevant; the number of people who are going to make their own independent implementation is relatively small. In this sense the spec audience is not quite the same as that of a spec for a programming language, which is important not just for compiler implementers but also for programmers in general.

That said, I do hope that ISO will change its policy to put specs behind a paywall.