Like how Apple stopped using up to date the GNU tools in 2008 because of GPL3. That moved showed me then that Apple did not want you to use your computer as your computer.
And of course, they won't share with each other. So another driver would be fear of a slight competitive disadvantage vs other-big-tech-monstrosity having a better version.
Now, in this scenario, some tech CEO, somewhere has this brilliant bright spark.
"Hey, instead of dumping all these manhours & resources into DIYing it, with no guarantee that we still won't be left behind - why don't we just throw 100k at the original oss project. We'll milk the publicity, and ... we won't have to do the work, and ... my competitors won't be able to use it"
I quite like this scenario.
People need to think about what licence they want to use for a project.
So not only would ffmpeg have multiple uncovered vulnerabilities, they would have less contributions and patches and less money for funding the maintainers. And for what? To satisfy the unfocused and mistaken rage of the peanut gallery online?
That's only one possible benefit.
Another could be to gain leverage on big tech companies via dual licensing. If Google, Amazon, etc want to continue using FFmpeg without forking, they could do so by paying for the old LGPL license. It would likely be cheaper than maintaining a fork. They'd also have to release their changes anyways due to LGPL if they ever ship it client side.
So the incentive to contribute rather than fork would remain, and the only difference is that they have to pay a licensing fee.
Ofc this is probably just a fantasy. Relicensing FFmpeg like this probably isn't easy or possible.