I'm sure it has something to do with Bandcamp's policies. For example, for name-your-own-price albums, Bandcamp accepts 200 free downloads. After that, the make the bands charge something (anything, really).
Amen. The early '80s hardcore punk scene is nice study in irony. The scene had a lot of bands that were (at least superficially) anti-capitalist, but the scene also serves as a perfect example of why the free market works.