The litter isn't the target; it's the feces buried underneath it. Referred to as coprophagia, eating feces occurs because dogs can smell food through the feces — in this case, cat food.

Dogs require different nutrients than cats, and eating cat food regularly can make them sick. However, you usually don't need to worry if your dog eats a few bites of cat food here and there.

When adult dogs eat poo, pups may copy ... “I noticed right away that my cat litter boxes were off. Suddenly there was no cat poo. Then it dawned upon me that Zoe was eating it.” ...