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.
Providing a real CVE is a contribution, not a burden. The ffmpeg folks can ignore it, since by all indications it's pretty minor.
If it's to fix vulnerabilities, it seems within reason to expect a patch. If the reason Google isn't sending a patch is because they truly think the maintainers can fix it better, then that seems fair. But if Google isn't sending a patch because fixing vulns "doesn't scale" then that's some pretty weak sauce.
Maybe part of the solution is creating a separate low priority queue for bug reports from groups that could fix it but chose not to.