The version numbers used as tags within the repo began life reflecting a single overall version number of the entire repo, being identical within all crates. This was never expected to become a problem, not expecting so much work to end up being done here, and for binding and sys crate versioning to diverge so much.
Since version numbering of crates started to diverge, version tagging remained associated with the “higher-level” binding crates. Furthermore sometimes minor versions of the less commonly updated simple and glib-mainloop crates are skipped over to keep versioning inline with the main crates, to try to keep some sanity.
I am aware that this setup is an unfortunate potential source of confusion now.