Because the instinct of dogs is to pick up things to eat everywhere, and human feces has certain nutrients, which are very needed for dogs. The ancestors of dogs, wolves, lived in a very harsh environment and often did not have enough to eat. Only then will they eat some food that we humans cannot understand, and dogs retain this habit of wolves.

Tip:

If we want the dog not to eat poop, we can train it from an early age. Of course, the most important thing is to make the dog eat full every meal, so that it has no appetite to eat. Shit.