It's a well-proven cookie-cutter formula. It works. The entry level is a bit lower than it is for something like McDonald's. There are very clear directions on how to operate a Subway franchise. At the same time, the people owning the stores tend to be very entrepreneurial in their focus.
They see an opportunity to develop a business and create wealth. Unlike a lot of small cafe and restaurant owners, they're not people who've bought into a lifestyle choice. There's no emotion or ego involved. And from a business point of view that's an advantage.