Making a profit is dependent on the franchise, the location and many more factors. I am not familiar with all franchises but most you can make a comfortable living but you will not become rich by owning just one franchise. Since the owner knows the requirements of a franchise, they often own multiple franchises. they know what to expect therefore they can determine if theft is taking place, they know what the operating margins should be etc. Often the franchisor likes to sell more franchises to existing franchisees because they know how you operate and if you are a good franchisee.
In theory, if you own more than one location, and hopefully you have picked profitable locations, the profits of all locations in theory will be greater than having just one location.