It does seem to have blown up as of late, hard drug usage was never glorified to the extent it is now.
The late-80s/90s Afrocentrism helped push back drug usage with the exception of marijuana, but it seems like 80s babies, and rappers who were kids during the crack epidemic took to hard drug usage more than previous generations.
Some of the biggest rappers right now are hard drug users: The Weeknd, Lil Wayne, Future, Young Thug, Danny Brown Eminem, Lil Boosie, Joe Budden, Kid Cudi, MGK, and a lot of newcomers like Rae Sremmurd, Lil Herb, GunPlay, Chief Keef.
It just seems like as hip-hop culture has been devalued, and the influence of the young White fans has increased, so too have the rapper's "secret problems" come out in their uncreative and hamfisted lyrics.