It's just something I've noticed.
Everything is politically correct now. Older strips like Beetle Bailey, Wizard Of Id, and Hagar the Horrible are no longer funny because certain things can no longer be done or said, cause either NOW or Amesty International would be pissed off about it.
That's why "Andy Capp" could not exist today. It's like Homer Simpson said: "Ah, Andy Capp, you wife-beating drunk!"
NOOOOOO, things have to be PC, and we have to LOVE and CARE for each other now, and we have to have TOLERANCE and COMPASSION for everybody and everything now!
"I have the right to not be tolerant of others if they are weird, they make me mad, or if they are different from me."---The Bad American, pre-9/11.
That was the clincher. 9/11. The country's DIFFERENT now. We have to be NICE to each other!
Oh well. Life DOES go on.....
Some of the cartoonists from the strips you mentioned are deceased and have been taken over by newer artists. That probably explains some of it too.
Another way funny comic strips lose their humor is when they morph into soap opera strips. Funky Winkerbean and 9 Chickweed Lane are prime examples of this.