Hello @RumplyPlatypus, welcome to the Spotify Community!
Spotify wants all the world's music, and they're working hard on making this happen for you. However sometimes agreements can’t be reached with the artist or label or a change may happen in music ownership. You can find more info here: https://support.spotify.com/using_spotify/search_play/content-missing/
Hey there you,
Yeah, you! 😁
Welcome - we're glad you joined the Spotify Community!
While you here, let's have a fun game…