The gravity model predicts that the optimal location of a service is

The gravity model predicts that the optimal location of a service is directly related to the population of people in a given location and inversely related to the distance people must cover in search of it.

An optimal service is directly dependent on the size of people in that given area. The larger the people the larger the customers and vice versa.

If the place is far then less people will patronize because people won't be willing to go through such stress to get such goods or services.