> Could they not have upstreamed those features in the first place?

Hard to say without being there, but in my experience it's very easy to end up in "we'll just patch this thing quickly for this use case" to applying a bunch of hacks in various places and then ending up with an out of sync fork. As a developer I've been there many times.

It's a big step to go from patching one specific company internal use case to contributing a feature that works for every user of ffmpeg and will be accepted upstream.