As far as I can see, the latest "new upstream" upload to unstable was
in "2021-08-25" which is more than an year from now, post which there
have been few bug fix uploads.
More notable upload has been the one that enables gstreamer support
I'm not sure if this is what you are pointing towards with "hasn't stood still"
https://tracker.debian.org/news/1306307/accepted-pulseaudio-150dfsg1-4-source-into-unstable/
Ofcourse the maintainers of this package are doing an excellent job
but from upstream release pov, it is still kind of standing still.