Out here in deep rural America where I live, the main door to most houses is the back door. You enter and leave through the back door. The front door is vestigial, it leads nowhere, it is hardly ever used, and indeed I know of houses around here where furniture is blocking access to that unused front door.
I grew up in town, where people use their front door as a front door, so all this is somewhat unusual to me. Not that I was unfamiliar with it: my grandparents' farmhouse had the back door as main access and exit. But still, back door as main door is a somewhat peculiar custom if you think of it. Or so it's always seemed to me.
Oddly enough, my house, on a gravel road way out here in the country, has the front door as main door. This house was built about 1880, and apparently the front door has always been the main door. I know of one or two other houses in the area which also are structured so as to make the front door the door you mostly use. But such houses are very much in the minority, out here in the wide open spaces of Back Door America.