YT Music has music as a first class entity where Youtube itself does not and cannot, so it has features like related music, "radio" playlists based off a track,

YT Music has music as a first class entity where Youtube itself does not and cannot, so it has features like related music, "radio" playlists based off a track, music recommendations, playlist generation, artist pages with a top 10 song list, and other features you expect from its competitors.