Shoes on shoes off

Why do Americans wear shoes in the house and why do Canadians not? To come to Canada and walk all over somebodies house and not take your shoes off is so rude and to go to the states and take your shoes off at somebodies house- you are looked at funny and thought to be making yourself quite at home. I don't get the difference? How often do americans have to replace there carpet? Being that we have cream carpet I know how dirty it gets even when I don't where shoes.