Hey @GoLoo, welcome to the Community!
Spotify only adds music that artists/record labels give permission to be added. The awesome thing is, Spotify is always working to add new music. I love checking out the New Releases section to see what all has been added. If you want to get a song added to Spotify, the best thing to do is to contact the artist or their record label directly and ask them why the music isn't available, since ultimately it is up to them whether to allow Spotify to publish their music or not. Another thing you can do is fill out this form letting Spotify know what you want added. That won't guarantee the song will be available, but it helps Spotify guage interest in artists and could help them add songs like the one you've mentioned.
Hope that helps, let me know if I can do anything else!