Looking at the changes and fixes in recent releases of the Closure library, it sure doesn't look abandoned or even practically abandoned. I think I understand what you mean though. The Closure library looks good at what it does, but doesn't have a big ecosystem around it like React or Angular.

I remember looking at the Closure library back in 2010 and decided against using it, but from what I can see it still looks pretty decent. It doesn't look as nice to use as Angular or React, but it's been around a lot longer than either of them and probably has to remain backward-compatible with some pretty old code.