Can you provide link to Spotify's app store? I've used spotify since it launched and was never aware of this feature.
The main issue was if you want to make a commercial app, there are no publicly available commercial terms, and it is easy for Spotify to not offer commercial terms to apps/companies that may in some way increase the chance of competition with Spotify. For example, if you wanted to make an app that would allow you to export your playlists, Spotify may offer you terrible commercial terms or none at all.
This is more restrictive than Apple.
https://www.iorad.com/player/2097656/Spotify---How-to-view-S...
Due to the way music licensing works, Spotify would never have had the same type of app store as Apple or Google.
The main point is, Spotify has a platform, like Apple, but is throwing stones from a glass house when it comes to trying to build on the platform.
Most of the integrations do not have anything to do with using the copyrighted music, e.g. a playlist export app.
Most of the integrations do not have anything to do with using the copyrighted music, e.g. a playlist export app
Most Spotify integrations literally involve playing music through Spotify, so it's curious that you pick one of the very rare integrations that do not.