Freestyling meant freestyling
The craft of rap once required—yes REQUIRED—multidimensional, varied abililties. Not to harp on "the art of the MC" here, but let's think briefly about freestyling: gone are the days when one could lob five words, chosen at random, into the air for a mic-wielding poet to transform into an off-the-cuff narrative. Sure, the bars weren't always vicious (some folks, like Supernatural, employed stock phrases that helped to fill out his freestyles), but the infinite possibility and risk made it all so entertaining—and above all, was a proving ground for rap performance.
When 8 Mile exposed battle rap to the masses, the tide was already turning; the film completely flipped the free-flowing contests into a theater for pre-written punch-lines. Outside of performances, radio offered the best opportunity for DJs and listeners to test an MC's capability; if a rapper rehashed a 16 from an album, it was flat-out unacceptable. We needed to know if our rappers could actually rap.