I've done a lot of exploring into the spotify catalogue regarding more obscure bands from the 60s and 70s in particular and there are simply a ton of albums that aren't there. I'm talking really well regarded albums in enthusiast circles that are not there. Now the issue I have is that you can basically go to youtube and type in "(album artist) (album name)" and find a stream of any album ever. I still think spotify's organizational features are really useful but I can understand why they don't have a lot of subscribers when youtube is just ridiculous with it's music streaming right now. How can spotify survive when youtube has everything?
some examples of missing albums that are available in full for free on youtube: Museo Rosenbach - zarathustra, Harmonium - all albums, banco del mutuo soccorso - all albums, Kraftwerk - early albums, all german album versions, magma - felicite thosz, slag tanz, faust - s/t, so far, ash ra tempel - all albums, amon duul ii - phallus dei, popol vuh - in den garten pharaos, yezda urfa - boris..even genesis' the lamb lies down on broadway, a famous album is not there but is on youtube.
and that's just a cursory search off the top of my head for obscure stuff. I mean spotify is unmatched for classical and jazz but they are really lacking in a lot of areas.