There is much much more to the code base than simply youtube ripping, both can (in theory) also rip from (say) ABC Australia's iView, from the Royal Institute Christmas Lecture series, from redtube, etc (hundreds and hundreds of variations of websites).
That shim layer between the core ripping engine(s) and the manifold ways of embedding access to a stream is what is being kept current in yt-dlp releases (and -U updates).
Original most recent official youtube-dl (December 2021 release) can no longer find its update service.
yt-dlp still claims to keep track with the parent project. Most would use it for the additional functionalities it provides over youtube-dl.