Rap quickly evolved year over year starting in the early 90's before it blew up and went fully mainstream
This is the answer. Rap evolved extremely fast back then
Drill/Trap lasted for years and years in this modern era
Back then, popular rap styles typically had a shelf life of a couple of years. That's why guys like LL get so much praise for longevity.
Absolute facts, 100% agree with this
1978 - 1981 - Disco Party Rap
1982 - 1985 - Run DMC/LL Cool J/Early Def Jam scream loud on the mic aggressively rap
1986 - 1989 - Rakim/Kool G Rap/BDK multi-syllabic rhymes rap
1990 - 1993 - West Coast Gangsta Rap and Tribe/De La Soul/etc alternative Rap
1994 - 1999 - East Coast Mafioso super lyrical Rap
Wasn't until the 2000s did you see Rap styles and Eras slow down and actually take a decade to expire. Hip Hop game was brutal pre-2000 to try to keep up with the styles. Back then, rappers like Run DMC, Kurtis Blow, BDK, Kool Moe Dee, sounded outdated when they were only 27 yrs old. Nowadays rappers can have long careers into their mid-40s