It is well documented. It is also ridiculously aggressive.

If it wasn't in the Java ecosystem, it might not feel weird. But the Java community had maintained backwards compatibility for a long long time. Guava promises, what, a year?

And for internal use, that is fine. I have seen some poor sods introduce it as a dependency of theirs, which can lead to frustrating upgrade cycles.

Edit to add: the Jakarta libraries are also fairly well designed. To the point that most things in guava were already there.