I pay for YouTube Premium but Vanced was still appealing because it removes other things I don't want, like posts in my home feed, Shorts, YouTube Originals and sponsored segments of videos.
Vanced is about giving the user what the user wants, instead of what YouTube wants the user to want.
Not to mention sponsorblock - not that i use it, but i can understand people who do.
...and some people aren't content with that