The staff ate it later

Restaurants (at least in the US) have very strict standards about how long you can keep something at room temperature before you have to throw it away. Those standards are extremely conservative, and lead to a lot of food waste, but if I were on the staff I'd at least want to keep an eye on how long something has been sitting out. Those standards have just been beaten into me.

You also see that on a lot of fictional TV shows with dining scenes. Often nobody actually puts anything in their mouths. It was made hours ago while you were off shooting something else, and still more time while they got costumes, lights, makeup, etc. right (and for several takes). By the time film is rolling it has gotten quite gross.

(Assuming it was even food in the first place. Fake food often looks better and doesn't go off.)

That and nobody wants to eat a meal 40 times to get 40 takes.

This is the answer. The food is perfectly fine. It's fresh, there's catering on set, and it can be replaced as needed, unless it's something super unusual.

BUT if you eat the food in one shot you need to eat it in all the shots for continuity, so you can edit it together. Get ready to start barfing after 40 big bites of the same damn thing.

If you look closely, you'll also see the coffee/tea cups actors sip from are usually empty. Can't afford the risk of accidentally spilling liquid on the costume and delaying the shoot.