Why is the door rectangle?

I think it is the best shape for the human body to pass through. A round door would be very hard to construct in order to come in or pass on it one need to bend. Square door will be in need of more space and need more wood for its length so why pay for more wood if its not necessary. Oval door one should step up into the house. Doors are not only created for human to come in sometimes we use them also for furnitures. Best shape architects invented that resemble to human was the shape of rectangle.