Two factors:
As a former Arizona resident (25 years in various places around the state), I will note that the decline in AZ's political culture began with a massive influx of Californians, starting in the 1970's but exploding in the 1990's. As property values went through the roof on the west coast, many Californians sold their houses and moved to AZ to "trade-up." They brought their left-wing politics with them. When I go back to AZ to visit, I barely recognize the place any more.
Second, McCain originally ran for office as a Barry Goldwater Republican -- strong on national defense issues and (more or less) libertarian on social issues. He fell in love with Washington and the Beltway culture (especially media types) and "went native." He actually started to believe his own press. Gradual process that intensified over the years.
Thanks for the insights. Much appreciated.