Experience

Since 1963.
President -------------- Highest Previous Job
Lyndon B Johnson----- Vice President
Richard M. Nixon- ---- Vice President
Gerald R Ford--------- Vice President
Jimmy E. Carter Jr. --- Governor of Georgia
Ronald W. Reagan ---- Governor of California
George HW Bush ------Vice President
William J Clinton ----- Governor of Arkansas
George W. Bush -------Governor of Texas

See a pattern?

I guess the American public value experience in their Presidents.