I'm in the WG14, and I, like you, only use c89. So why does c23 matter? Well in terms of features it matters very little but a big part of wg14s work is clarifying omissions from previous standards. So when c23 specifies something that has been unclear for 30+ years, compiler developers back port it in to older versions of C where it was simply unclear. It matters a lot for things like the memory model and things like that.
> compiler developers back port it in to older versions of C where it was simply unclear
You cannot rely on that. If you're maintaining C90 code, with a C90 compiler or compilation mode, you should go by what is written ISO 9899:1990, plus whatever the platform itself documents.
We actually don't want compiler writers mucking with the support for older dialects to try to modernize it. It's a backward-compatibility feature; if you muck with backward compatibility features, you risk breaking ... backward compatibility!
C cares a hell of a lot about backwards compatibility. Whenever there is a corner case that gets fixed, the number one goal is to retain compatibility. most of the time, these clarifications clarify what everyone is already doing and has been doing for decades.
Also, most of these corner cases are so obscure that the vast majority of people with decades of C experience have not encountered them. C is an extremely explored space.
At least for C++ there is something called defect reports. When agreed, those defect reports to retroactively applied to previously published C++ standards.
