Record companies made a push to crack down on mixtape releases in the mid 2000's, even going as far as trying to pin DJ Drama (gansta grilllllllzzzzz) with a RICO charge, for illegal distribution of music owned by the rappers record companies.
http://mobile.nytimes.com/2007/01/18/arts/music/18dram.html?...
A lot of these guys, didn't even want to fuck with the big labels, because they didn't get anything from them. The money they would receive from a record deal, could be just as easily made by selling merch, and going on tour, all without having to pay back a record advance.
Unfortunately, Apple has figured this out. Rappers are now signing deals for their mixtapes to be iTunes exclusives for a few weeks, and Apple with all their force, is cracking down on sites like datpiff for releasing the tapes they have exclusive rights too.
Young Thugs brilliant Slime Season trilogy was released on datpiff up until the third installation. Apple got an exclusive.
Just hope this amazing ecosystem doesn't disappear...