Original Six?

A Bicycle tour of all the NHL arenas would have been much simpler between 1942 and 1967. Why is it the original six? The Original Six is the term many hockey fans use to refer to the six franchises playing in the early days of the NHL from '42-'67. Detroit, Chicago, New York, Montreal, Toronto, and Boston. Why aren't the Ottawa Senators considered original? Granted, they were without a franchise for many years, but they were around at the beginning. Ottawa lost their franchise to St. Louis after the Great Depression.They were renamed the Eagles and disbanded in 1936. The Senators returned to the NHL in the 1992-93 season.
Original Six doesn't acknowledge the teams: Montreal Maroons, The New York Americans, and Pittsburgh's Pirates/Philadelphia Quakers; who all fell victim to the Great Depression.