In some areas of the world, this method seems to have persisted longer. Sahel Sounds released two compilations "Music from Saharan Cellphones" of tracks that they originally discovered on such bluetooth sharing networks: https://sahelsoundscompilations.bandcamp.com/album/music-fro...
(Though I'm pretty sure that they then went back and established traditional contractual relationships with the artists before releasing the compilations).
Man I remember drifting around the internet and finding the blog post about purchasing song .MP3s in a market and transferring them over bluetooth. At the time that seemed like such a cool and unexpected alternate evolution of purchasing songs from itunes.
(Though I'm pretty sure that they then went back and established traditional contractual relationships with the artists before releasing the compilations).