It also isn't cost effective for me to make the time to make my own food, even ignoring the cost of the ingredients; aside from simple things that use mostly non-perishable ingredients.
However, even going out to eat, the incentive to buy in bulk /there/ exists too. Purchase of a single meal that should fill someone up for a day has a substantial discount over getting what should be a properly sized portion for a small regular meal.
For all sides, the market incentives push towards over-consumption which is why we have the outcome we do.
I recall hearing that the cost of labor was actually one of the primary factors in meal price.