It's funny that the "obviously not causal" example is margarine consumption (USA) vs divorce rate (Maine), though I can see a possible casual reason
"Carnivore cool" has to be related to having excellent quality of nutrition
More margarine is related to the demonization of animal fat, those with higher margarine probably have lower quality nutrition thus more stress, which could easily increase the divorce rate.
I wonder what the divorce rate in carnivore couples is compared to vegetarian couples