Shake Shack began as a hot dog stand, but a hot dog stand created for a park being developed by a successful NYC restaurateur who owned a hospitality management company. If you're the sole developer of a new downtown park, and you own the only hotdog stand in that park, and you have lots of resources, it's going to be a success. When later there's the opportunity to develop the park further, you may pony up the cash to build a building to sell even more food. And later, when you see how successful it is, and you see the opportunity to branch out, you can do that, too.
Some restaurants become popular because people with money are in the right place at the right time, and not because it was an old-school authentic eatery discovered by a food writer and put on a top-foods-list.
Shake Shack is more about hyping just-ok products. There are better (and cheaper) burgers to be had without the megadosing of salt to compensate for a mediocre blend. They keep the seats filled because they worked the hype machine and the tourists flock there.
Some restaurants become popular because people with money are in the right place at the right time, and not because it was an old-school authentic eatery discovered by a food writer and put on a top-foods-list.