Most of them would just pirate in the old days, and most FOSS licences give them clear conscience to behave as always.
1) dedicating compute resources to continuously fuzzing the entire project
2) dedicating engineering resources to validating the results and creating accurate and well-informed bug reports (in this case, a seriously underestimated security issue)
3) additionally for codecs that Google likely does not even internally use or compile, purely for the greater good of FFMPEG's user base
Needless to say, while I agree Google has a penny to spare to fund FFMPEG, and should (although they already contribute), I do not agree with funding this maintainer.
Equally there is no requirement on ffmpeg to fix these CVEs nor any other.
And, of course, there is no requirement on end-users to run software from projects which do not consider untrusted-input-validation bugs to be high priority.
I see this sort of sentiment daily. The sentiment that only what is strictly legal or required is what matters.
Sometimes, you know, you have to recognise that there are social norms and being a good person matters and has intrinsic value. A society only governed by what the written law of the land explicitly states is a dystopia worse than hell.
If you find yourself with potentially serious security bugs in your repo, then the social norm should be for you to take ownership of that because, well, it's your repo.
The socially unacceptable activity here should be treating security issues as an irritation, or a problem outside your control. If you're a maintainer, and you find yourself overwhelmed by genuine CVE reports, then it might be worth reflecting on the root cause of that. What ffmpeg did here was to shoot the messenger, which is non-normative.