This is false. It's not abandoned. There are many commits per day and that wouldn't happen without a dedicated team [1]. There are frequent releases with impressive-looking changes [2].

But this does look like a team that's focused on the needs of Google's internal customers? An external-focused project would have better docs and do more outreach.

[1] https://github.com/google/closure-compiler/commits/master

[2] https://github.com/google/closure-compiler/wiki/Releases