what's the meaning of "All that food won’t eat itself"?

One or more people is/are needs to, or is being invited to, eat the food., or possibly it has been prepared in error for people who will not eat it.

Idioms of the type "[something] won't [perform an action] by itself" are used to state that someone needs to perform the action. Often there is an implied rebuke for oversight, slowness, or laziness, etc.

That fence won't paint itself = someone needs to paint the fence.

Your homework won't do itself = you need to do your homework.

The car won't wash itself = someone needs to wash the car.

Steve Bannon won't blow himself, or will he?