We once had a guest lecturer who broke down the ROI of making the ladies bathrooms beautiful (but not the men's). Presumably it leads to more alcohol consumption, which is where the margins are. I think restaurants in the UK make almost no money on the food itself.
In some places, the drink is the loss leader. A group of people head out to a place and pay the minimum - a $0.50 cup of tea. One of them will buy a basket of snacks for the group. Someone in that group might order the food. A plate of noodles or naan is nearly free in terms of ingredient costs.
Sometimes it's the atmosphere. I'm not sure if other countries have this, but there might be a major game on TV - football, wrestling, etc. Not everyone can afford to watch it at home, so everyone goes to a cheap restaurant. Sometimes the people who do have it at home just go to hear the cheers.