Perhaps it's the fact that there are so many moving parts to coordinate on a gridiron and/or the fact that it's more difficult for a single player to dominate a football game the way one can dominate on the ice, hardwood or diamond. Whatever the reasons, there's no doubt that football is the most difficult sport in which to win multiple back-to-back titles.
In fact, numerous three-time consecutive champions exist in every major North American sport ... except for football.
In the NBA, the Boston Celtics set the standard with eight straight titles from 1959 to 1966. In the last 14 years alone, three teams have won three consecutive titles (Chicago, 1991-93; Chicago, 1996-98; Los Angeles, 2000-02).
On the college hardcourt, UCLA set the standard soon after the Celtics, winning seven straight NCAA championships from 1967 to 1973.
In the NHL, the Montreal Canadiens set the standard with five straight Stanley Cup championships from 1956 to 1960. Three other teams won four consecutive Stanley Cups, including two as recently as the 1970s and 1980s (Ottawa, 1903-06; Montreal, 1976-79; N.Y. Islanders 1980-83). In a 21-year period from 1968 to 1988, just five teams won Stanley Cup championships (Montreal, 9; N.Y. Islanders, 4; Edmonton, 4; Boston, 2; Philadelphia, 2).
In major league baseball, the New York Yankees set the standard, winning five straight World Series titles from 1949 to 1953 and four straight from 1936 to 1939 (the Yankees won 16 out of 27 MLB championships from 1936 to 1962) and three straight from 1998 to 2000. Oakland also boasts three consecutive championships, from 1972 to 1974.
Further evidence of the difficulties inherent in football is provided by the college game. Since the AP poll was established in 1936, there has not been a single three-time consecutive champion in Division 1-A college football.