They are hard to discover… and hard to use.
Flippin' fantastic, that's exactly what I want out of my documentation tooling.
I absolutely agree it would be better if forge data were part of the repo itself rather than separate. But for teams that are using a forge in the standard way, they should rely on the forge for this sort of thing, rather than hide important information in an obscure git feature.
My point is that "the comments aren't accurate" is also a people problem. And I absolutely disagree that commit messages are "documentation" of anything except the development history.