There's some non-intuitive economics going on here.
The biggest driver of restaurant meal prices isn't the ingredients, it's the cost of maintaining the building (paying rent), utilities, preparing the food, serving it to you, and cleaning up after. If they cut the portion in half, it will still cost almost as much to prepare it and put it on your table. Apparently, a critical mass of customers get upset if the portion is "too small" relative to the price. So ... they give you a huge portion. And they don't get upset if you take half of it home for lunch.
Yeah, I get it. I have 18 years of Retail Management behind me. ‘Food Service’ is just ‘Retail’ in a fancy dress. ;)
I ordered a pasta, chicken and veggies dish. It came in a BEAUTIFUL ceramic bowl - that was AS BIG AS a 2-Quart casserole dish that I’d use for a family-sized meal! The serving vessel was gorgeous - wish I could’ve taken THAT home, too. ;)