If you want to fix up old codecs in ffmpeg for fun, would you rather have a list of known broken codecs and what they're doing wrong; or would you rather have to find a broken codec first.
While true, Only Google has google infrastructure, this presupposes that 100% of all published exploits would be findable.
What a strange sentence. Google can do a lot of things that nobody can do. The list of things that only Google, a handful of nation states, and a handful of Google-peers can do is probably even longer.
Google does have immense scale that makes some things easier. They can test and develop congestion control algorithms with world wide (ex-China) coverage. Only a handful of companies can do that; nation states probably can't. Google isn't all powerful either, they can't make Android updates really work even though it might be useful for them.
[1] https://security.googleblog.com/2014/01/ffmpeg-and-thousand-...
Not really. It requires time, ergo money.
Making the vulnerability public makes it easy to find to exploit, but it also makes it easy to find to fix.