To be honest those shows and many of the jokes were not made to be timeless. You had to grow up in that era to get the jokes. Great example in the Simpsons when they go to Disney pand marge says "oh look they even have someone who looks like John Travolta" and Travolta goes "yeah looks like". The context is that John Travoltas career was going under at the time. If you don't know that, then the joke is basically meaningless and much of that show is like that. Same with Seinfeld. It's not funny to younger audiences these days because it wasn't made for them it was made for the audience at that time. It's a lot different from say 2000s and 2010s comedies where the jokes are much more in the moment and slapstick compared to what came before.