Why? They do not need to eat. The reach out for the succulent flesh of humans even when they lack mouths and stomachs. Would a pair of zombie lips and teeth nipple endlessly on what ever came in range?
That’s a rhetorical question.
This mysterious craving, much like the zombies that display it, can’t be explained by mere mortal science. They are the dead and in that capacity they must always consume life.
Brains seem to be what the garden variety undead desire most of all. This might be what we look like to them.
Zombie scholarship speaks to this point:
The deactivation of a zombie's nervous system, caused by possible chemical and genetic alterations, has often been used to explain their very low mobility and rate of metabolism. The chemicals in the human hypothalamus, found in the brain, act as a stimulant for their metabolism, prolonging their not-quite-dead condition. That make the brain highly sought after in the random wanderings of the living corpse.
I wonder if they would like sesos.
I don't. It tastes like old cheese.
So when you take your sweet smelling living brain out on the town please be careful who you hang with
"Just drop the brain or I'll use this!"
and bring fire,
-GH