One tool that does everything. Its literally backwards. It eventually always results in one tool that's constantly broken. There should be a tool for each site if there is a maintainer who actually cares about that site.
This is misapplying the unix philosophy. There would be too much duplicated functionality between different tools for different sites. It would be like having different versions of /bin/ls for different file systems.
To follow on, it's a valid point though. /bin/ls can handle different file systems because many other separate people/projects are responsible for the file system specific support (in the kernel).
Youtube-dl should be architected to allow many other people to own the site-specific support (i.e. via a plugin system, with the main "distro" of yt-dl including some popular plugins, which other people or themselves are responsible for), if it was like that then probably this fork wouldn't be necessary.