Well, isn't Spotify a paying service? At least I think it is.
Spotify has both a free and a paid version.
On PC, there isn't much of a difference between Spotify Free and a paid subscription, except that you get ads. I find Spotify Free more convenient than Youtube, because everything is nicely sorted on the artist's page, and playlists are more manageable.
On mobile on the other hand, Spotify Free completely sucks. You can't just listen to a song, you can only listen on shuffle mode. So if you're on mobile, Youtube is a lot better than Spotify Free. However, Spotify Premium on mobile has a big advantage over Youtube: you can listen to music even when your phone is locked or when you're using other apps. That's why a lot of people do subscribe to Spotify Premium.