Could you explain more about it? I assumed the maintainers are doing it as part of their jobs for a company (completely baseless assumption)

Reupvoted you from gray because I don't think that's fair, but I also don't know how much there is to add. As far as why I'm contributing, I haven't been socially involved in the ffmpeg dev community in a decade, but, it is a very reasonable floor to assume it's 80% not full time paid contributors.