Spotify is always open to new music, and would like to have all of the tracks ever composed. Though, this is not possible. It's the labels, the artists who make this happen: it's their choice whether to upload the release to Spotify or not, it's them who knock this awesome streaming service's doors in order to find a place where every tune belongs.
So - your best choice is to contact either the artist or the label, and ask them why the release isn't on Spotify: they'll be able to provide you with the explanation you need: who knows the actual situation better than the rights holders?
Hope you get a fast response, and enjoy Spotify to the fullest!
However, if you look at certain CDs of the same artist, namely, Falco 60, it does contain the title song of Wiener Blut. The compilation is a new release and probably that's why it is available only to the paying customer. Tracks like Garbo and Tricks, from the same album Wiener Blut, which are featured in Falco 60, are also unavailable to free listeners. So it appears not to be a matter of choice as to what to upload. What do you mean by upload anyway? 🙂
It is also interesting to note that the album Wiener Blut is absent from the database of certain competitors providing music streaming services, too. I am puzzled as to the reasons for it. I can understand, for example, why the recordings of the KLF are not generally available. You can read about it on Wikipedia indirectly.
Incidentally, a track titled The Sound of Music is also not available in Falco 60 to free listeners but the same track can be listened to without any problem if one goes to the original album Emotional which the song came from.
So, essentially, some tracks are and are not available at the same time. It is a bit puzzling but can still be solved by buying CDs and LPs for one's collection at any time.