Jim Thorpe was a popular athlete at the time and helped add credibility to the sport. The league grew between the 1920s and 1930s but stopped signing black players in 1927. When World War II ended the leagues were reintegrated. Major changes followed the war, including the implementation of a commissioner which resulted in franchises being more financially stable. After starting out with 10 teams in 4 cities, the league has expanded to its current number of 32 teams. Many labor agreements and large television contracts have led to exponential profits for the NFL. (Pro Football Hall of Fame)
U.S. civil rights attorneys Cyrus Mehri and Johnnie Cochran studied how black coaches were less likely to be hired and more likely to be fired than their white counterparts, even after having higher winning percentages. The purpose behind the rule was to make sure that minority coaches would be considered for high-level coaching positions. (Wikipedia) The NFL saw an increase in the number of coaches of color the year after the rule was implemented.