Until 1945, Americans did not even embrace Pizza. There were pizza restaurants here and there, but they were not known well by Citizens in North America (Sort of like how the greek dish the Gyro is not known well in America today). American and Canadian soldiers returning from Italian service had tried local foods and Pizza was a favourite for the soldiers. Pizza spread by word of mouth and the American market grew to satisfy the demand for the dish, and eventually adopted it into society. As for the friday part I would guess people would rather party then cook and pizza is a quick and cheap food item that most people generally like.

Source: Uncle John's bathroom reader edition ? (Not a great source for history but it had this topic in it)