I'm not clear - are you saying most tunes you grew up with+new releases that excite you aren't on youtube? or that you think youngsters aren't clicking outside spotify?

Maybe it's just the genres I'm into but between youtube and soundcloud (+ a bit of bandcamp) maybe 95% of underground music new or old that I look for is available. Knowing it exists in the first place is a step of course but once you find something good both sites seem pretty good at suggesting similar tracks.