Cavemen was just too intelligent
As soon as the first episode aired, I told my wife "This will be cancelled". Not because it was bad...to the contrary...it was too intelligent for the average viewer. It wasn't all obvious flatulence and anatomical size jokes, so people didn't think it funny. I, personally love dry, have-to-process-it humor.
It falls into the same category that "Sports Night" was in, shows for guys, assuming they are half way intelligent.
I hope one of the cable networks sees the value and humor of this show, and revives it.