When submitting a third party package to the repo you become the third party package maintainer. And it's your responsibility to make sure you don't break the world when updating it. If people using it want a newer version (only one version can live in the repo, by policy) it is generally their responsibility to manage that transition. It's been a long time since I managed a third party package, but that's my rough recollection.

The other thing is that third party packages are checked in as source. Everything is built from source at Google.