There are several reasons we cook more food than before: More money. Less time. Two working parents. Better refrigeration.
Until recent generations, the "typical" family had a working spouse and a cooking spouse. Today, one form of the modern "typical" family includes a working spouse and a cooking-and-working spouse, and for them, the ability to preserve leftovers is a welcome relief from everyday, every-meal cooking. And besides less free time, two working spouses also means more money to buy more food.
With modern refrigeration, per capita calorie intake has doubled as more of what we grow reaches the market and more of what we buy reaches our stomach. We no longer worry about making too much, and quite often, a few extra guests could appear and no one would suffer.
But in past generations, leftover food spoiled (high society searched the globe for spices to cleverly mask the spoilage), so a major effort of cooks used to be finding out how many would be present for a meal to plan for just the right amount. If the count was low, everyone took a little less. Maybe that sharing (and asking before taking the last tasty morsel) was good practice for life.
Perhaps, right after food preparation, we can set aside for leftovers and serve less food on our tables. Cook as much as you want, but serve less.