Remember when Family Circus didn't suck? Honestly, you probably don't, given that you're reading this blog (age demographic implies age less than 40 ;). Family Circus used to have some biting social commentary layered behind its "Kids say the darndest things!" demeanor.
Its hard to keep that kind of output going, Bil Keane obviously couldn't. His cartoons ceased being relevant and went to carp over the last 30 years.
Mommy, why does my cereal taste like bitter almonds?
The problem lies in the need of paper editors to fill space. Unless a new popular cartoon displaces a fallen one, paper editors will continue to carry a cartoon. Essentially, the dilemma of when to quit gets shifted to the cartoonists. Presumably, syndicated cartoonists haven't MC Hammer'd their lives and have more than enough cash to retire. So, they have the option of retiring with a good non-sucky repertoire, or they can just leech cash like Keane. I'm *not* suggesting a Kurt Cobain exit, just that with their money, they could leave depart the scene with a bit of artistic dignity.
Either I'm wrong about the money (doubt it), or artistic dignity does not rank too high with cartoonists (which tells you something about cartoons).