if they dont provide people with this amount of food they will say they arent getting their moneys worth.
and gave you ever heard of a ‘doggy bag?’ you dont have to eat everything in a single seating.
Mass market restaurants (no pun intended) are in an arms race with regard to portions. If they decided to serve normal portions it would indeed be a suicide mission on their part.
Problem is, with the foods they serve, they aren’t real good for warming up the next day. I could see three or four people buying all of those things and splitting them.