Those aren’t REST APIs to gather data about songs or your history. They are native APIs to control Spotify app on that machine etc.
I think a fair amount of their business relies on gathering data from people and recommending music. They don’t let 3rd parties to do that.
Re:Open-Source Spotify App
by sologuardsman2 on Tuesday December 24, 2019 @01:40AM
(#21870336)
Perhaps, but they also have APIs for song data and user listening preferences. It's actually pretty impressive how accessible their platform is to developers.
https://developer.spotify.com/documentation/
https://developer.spotify.com/documentation/ios/