before, dj used to sell those mixtapes from the back of their cars. kids would get new stuff, and new names (both djs and producers) would get chance to showcase their skills.. labels would pick some from those tapes...
but, it took them years to get out of the underground and get recognition, and equal worth as albums..
now, early mixtape djs are considered to be stars and labels are hiring them to put out their new releases on streets like that

now, lets get back on CD DJ-s.. there is more and more of them, lets not get into reasons why or do you like it or not.. they are here to stay, period.
lets say they want to play legal music. how many good compilations, unmixed is there on the market, so they can use it? how many good tracks isnt getting released on cds?