The genre really can lose its sense of humor. if you look at the late 60s, the funny sitcom almost died out, to be replaced by pleasant, unoffensive, but dull family fare. Even existing shows that had been funny early on, like My Three Sons and the Andy Griffith Show, just stopped trying to go for funniest. Then like a bolt from the blue, shows emerged again with broad characters who went for it - Mary Tyler Moore Show, All in the Family, The Odd Couple, Sanford and Son, MASH - it was an avalanche.

if you go into a sub for many shows, even older ones, it seems like at least the Reddit portion of the audience is quite humor impaired. Many posts express disapproval of acts, and even characters, as if the shows were somehow presented as exemplars of proper conduct. Comedy can't just run free if the writer has to keep that sort of audience in mind.