It isn’t just Maine, either, but most small town and rural areas in New England. We never used the front door in my parents’ house in MA except to move furniture because it led directly into the living room and stairs and there was no place to hang coats/remove wet shoes. In my current house in Maine, we actually do use the front door as the main entry, and have a gravel path directly from the driveway but it still feels a little weird to me!