My last dog prefered the cats food so we just feed them both on cat food, the dog last out the cat and lived 18 yrs, we even continued to feed the dog cat food after the cat had died as she wouldn't eat dog food.
Maybe some dog food manufacturers would wise up to this niche market and produce dog food that tastes like cat food. Could be a profitable new line.
Both My cat and dog eat each other's food. Basically what I think it is, is that cat food has more fat and dogs like it. I don't know why cats would like dog food though lol.
I guess they like it because the dog already ate their food thus they have nothing but dog food for their meal. Either they settle for that or go hungry.
I think it's just a simple matter of "the grass always looks greener in the other meadow". Or as the old Chinese put it "The neighbor's rice taste better".