The only thing which F-Droid reports is that it uses jawg.io for visualising the map tiles and that is considered non-free is because it is… commercial?
This is the quote from the Streetcomplete github:
Since mid 2020, JawgMaps provides their vector map tiles service to StreetComplete for free, i.e. the background map displayed in the app.
Personally I don’t care that much about FOSS/non-FOSS but IMO a reason like that is least of my concerns when looking at open source. If they’re providing a free (as in money) service to an open source app then that’s perfectly fine.
Unless Spotify drastically changed their backend it doesn’t make sense why firing one person will make algorithms stop working