Google is a significant contributor to ffmpeg by way of VP9/AV1/AV2. It's not like it's a gaping maw of open-source abuse, the company generally provides real value to the OSS ecosystem at an even lower level than ffmpeg (which is saying a lot, ffmpeg is pretty in-the-weeds already).

As to why they bother finding these bugs... it's because that's how Google does things. You don't wait for something to break or be exploited, you load your compiler up with santizers and go hunting for bugs.

Yeah this one is kind of trivial, but if the bug-finding infrastructure is already set up it would be even more stupid if Google just sat on it.