I think that depends on what rap you're talking about. The party themed rap that kids listen to today, I agree with.
Both Dre and Kendrick however have put out music on important topics that are relative to today's society. Dre in the 90's with stories about growing up in Compton and the difficulties he faced, and Kendrick, a Compton native as well, with modern-day stories of politics, discrimination and culture. Kendrick even won a Pulitzer prize for his last record, the first hip-hop artist to do so. David Bowie cited Kendrick Lamar as one of his biggest influences for his final album before his death, Blackstar.
Both lyricists are more articulate, personal, honest and important to American culture than the majority of rock and pop produced today. I think there may be a lot more people in their 40's and 50's who listen to these artists, especially in the LA area where they all grew up than one would think.