They had direct or indirect scene connections and got reliably high quality material. Lots of it. Like Oink amounts.
That's what I liked about the early service, they had so much obscure and niche stuff that it was fun and interesting to just browse and discover. Then the entertainment mafia bought in and they deleted huge portions of the catalogue, and I never returned.
Bandcamp was good until recently, now it's turning into a garbage dump for "AI" gunk.