(thesis help) Why are fast food chains successful?

In part, it depends upon where the fast food restaurant is located; for example, a McDonald's next to a college campus may frown upon students who regularly use their WiFi access from 6 p.m. Until 11 p.m. However, as long as a patron continues to order fresh cups of coffee or soft drinks every so often most fast food places really don't mind how long patrons stay,but after awhile most chairs and booths in places like McDonald's get rather uncomfortable.