Was just talking to my wife about this the other day
Around here - and I know Ohio isn't a hotbed of ethnic cuisine - all the Mexican restaurants have virtually identical menus, and 90% the same decor. You could take a dinner from any one of them and serve it in any other and not notice the difference.
Same for Chinese restaurants. They all buy from the same suppliers, everything from the ingredients to the stock photos they put over the menu.
Burger chains are at least trying to differentiate themselves.