The name of the game is risk mitigation. In this case, there are lots of ways to rip a singular track. They are usually slow because you record the audio stream from Spotify.
But if you could get the original file from Spotify's servers and decrypt it yourself, you could automate downloading your entire library, offline forever at source quality DRM free. Unfortunately, that is illegal and Spotify is going to dick them with lawyers. Pretty sure that's what happened to this project: https://news.ycombinator.com/item?id=25017167
History: after the developer decided to pivot from only being a tool to scrape the encryption keys needed to decrypt an individual song, the developer decided it would be a good idea to build in automating the downloading and also decryption of those files, instead of letting people develop that as a separate tool.
Developer and project has disappeared shortly after that decision.
They probably mean source as in "what you get from Spotify", as opposed to what you can record after Spotify has decoded it, which you'd have to re-encode.
If it weren't for all the legal agreements with copyright holders, I feel like spotify would already have an open playback API.