Why does my dog do this?

i know my pitbulls aren’t the smartest but they love to eat cat poop it’s drives me crazy. i even bought a cat litter box with a hole on top to try to keep them out but not so much. they are on a very good diet and get plenty of exercise. i don’t understand it they don’t eat their own poop. and i know it’s not healty alot of my time yelling get out the cat box why do they do this and is there anything i can do to make it stop bc nothing i’ve done works