They are contributing back, which is a good thing. Other companies just fork, fix, and forbid to contribute back.

Burning out maintainers isn't "contributing back".

Do you have any examples of Google submitting vulnerabilities and refusing to assist maintainers create a patch when asked to do so?

Wasn’t that a story with ffmpeg a few months ago? And people were getting roasted for even the suggestion that google should contribute patches?

People were getting rightly roasted for calling google a leech when A) google does donate money to ffmpeg and B) that bug was in a weird format google almost certainly has disabled so they're not reporting it to get free labor.