Thing is, for most people living in a large city and on a tight budget, it's not the cost of the ingredients that matters but the facilities to prepare them.
I once worked at a large web company located in the center of Paris and that had a free use kitchen. It took me less time (<1h) to go shopping and cook for a few colleagues than it would have for us to go to a restaurant, and cost the same as buying supermarket sandwiches.
Sure, but most people have food prep facilities at home, particularly for those who can't afford to eat out as much, so bringing in food in a lunch box is accessible to most.
I once worked at a large web company located in the center of Paris and that had a free use kitchen. It took me less time (<1h) to go shopping and cook for a few colleagues than it would have for us to go to a restaurant, and cost the same as buying supermarket sandwiches.