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.
Clubs would give us £10 per girl we brought in, but much more importantly (to us) give us a table bang in the VIP section and a few free bottles. We would aim to bring 10-20 girls with us.
The girls would go and mingle with other tables in the VIP area who were often men who'd paid through the nose for a VIP table (£1,000 a bottle for alcohol that generally cost less than £50 wholesale, and this was in the early 2000s), because generally they knew they were rich guys and they had free alcohol on their tables.
At several set points, the club would send our table bottles of alcohol with fireworks and make a big deal out of it, and all the girls would migrate back to our table for the drinks and high-fives, which would encourage the men with the actual money to then order their own bottles in the hope of luring the girls back.
The girls were (frequently American) university students who got a free night out hosted by people they trusted, in a venue with bouncers they came to know well, we got the immense social proof of being the people at the center of the VIP section surrounded by girls which helped our own love lives no end, the club spent a few hundred bucks on us but filled their VIP area with pretty girls, and finally the bankers who'd paid a huge amount for their VIP table got pretty young American university students to talk to.
I'm sure this is still a popular model, and we were very far from the only people doing it.
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.