Blindly updating ffmpeg without the app being tested for it is a recipe for disaster -- ffmpeg has made API breaks in the past, and that meant that when an ffmpeg system update was required, all projects depending on it would need to upgrade to the new API.

So often, a distribution would be held back on an old ffmpeg (perhaps patched with some of the CVE fixes by a distro maintainer who might not be familiar with the codebase) to isolate the churn of upstream.

flatpak lets app maintainers update at their leisure, which actually gets them on a faster update cycle.