When NWA started talking about crime, drugs, etc., that had rarely been done before in hip-hop; it was original. After NWA, suddenly EVERY rapper was talking about how gangsta they are, a trend that still continues.
When Dr. Dre introduced synthesizers to hip-hop via "The Chronic", synthesizers had rarely been used in hip-hop (Afrika Bambatta and Whodini did this too, but that was before hip-hop's burst into the mainstream). After "The Chronic", an entire wave of copycat producers with synthesizers caused a 'G-Funk' craze trying to sound like Dre.
Rakim started rapping in '86, bringing multisyllabic rhymes and unconventional flows to the genre. Since then, Rakim's style has become a staple in hip-hop lyricism.
I could go through a plethora of other examples. In short, originality always shapes a genre. Those concerned solely with popularity are just desperately trying to copy others' originality. And considering people don't remember producers like Dirty Red or rappers like Kool Moe Dee, it's pretty obvious paying attention only to popularity is a downfall.