Then the question must be asked: How did the unjust due start?  Well, that is a looooong conversation.  I think a better way to have this conversation is to look at Rap/Hip-Hops fun history.  See, rap started off in its early form by DJs.....well ,ONE Dj (Kool Herc) prolonging jams by buying two of the same albums and playing the breaks, going back and forth to keep the party going.  This technique kept going and eventually, people started to rap over these extended breaks.   These breaks were usually found on the 12" versions of singles.  Now people started looping these breaks and rapping over them.  Thus is born Rap Music.  

With this type of simple beginnings, it became easily approachable.

So as people started recording over these loops and breaks, no one thought over the legal repercussions. An essential loophole (or so they thought) was how sampling was not included in the copyright language of the time especially with digital recreation. Remember, just like Apple's Garageband can have the average joe make a song, these were just regular people having fun and saying stories/poetry over prerecorded grooves.  All you needed was a turntable and a mic.

So did the authors of the music own the rights when someone put the actual recording in their music?  Oliver Wang wrote beautifully on this matter:

When sampling technology and practices became hip-hop's musical blueprint in the late 1980s, the business and legal rules were a thoroughly gray area. Since the techniques created digital copies of source material, copyright holders could argue that unauthorized sampling violated their intellectual property. Those doing the sampling could argue they were repurposing fragments of recorded music to create something entirely new. Up until 1991, disputes around whose argument carried more weight tended to be settled outside of court.

Per usual. technology comes faster than the law. Similar thing happened when VHS came out.  Movie companies at first blocked it. Now movies like Frozen and Avatar have sold over 7 million DVDs and BluRay.  Let's just say the companies have changed their mind!  So now the court has to determine this gray area about sampling.  Oops.