There's a lot of inertia here, but also the tarball is or was the one point of commonality where you could say "this is the standard thing every upstream provid

There's a lot of inertia here, but also the tarball is or was the one point of commonality where you could say "this is the standard thing every upstream provides". Today almost everything has a git repo, but it still isn't 100% universal, and in the past even less so -- some projects had git, some svn, some cvs, some mercurial, some didn't use source control at all(!), but everybody provided their releases as source tarballs. So when you're designing a distro packaging workflow 20 years ago, "treat the source tarball as the authoritative upstream output" made sense, because it was the authoritative upstream release output.