I was gonna say that!
curl and ffmpeg are definitely commendable "100%" FOSS projects, but they aren't chasing new features. HTTP3 is big, but it's not like curl had to break HTTP 1.1 compatibility to add it. AV1 is big, but it's not like MPEG1 will ever change. Both projects deal in protocols, which means most of their requirements are literally set in stone, or silicon.
Whereas youtube-dl is constantly breaking _only_ because YouTube is constantly breaking, probably on purpose to thwart youtube-dl.
Why spend the other 80% of my time adding armor plating and documentation to a feature that will either be gone or half rewritten next week?