Unfortunately, that is not a decision made by spotify. I can assure you that Spotify wants just about every song in the world to be available on their platform, but they unfortunately do not have the rights to songs and therefore cannot make the decision of putting a song on the platform or even taking it off. It would be a decision made by either the artist or the artist's record deal. But hopefully Spotify will reach out to the record label and get the songs back on the platform for listeners :)
Songs availability depends on the artist and their label, not Spotify. Unfortunately, some tracks aren't available due to this reason, but Spotify would love to have all the world's content available there.