4. Phoenix - The city itself votes Democrat but not by the massive margins most other cities its size do so the Republican strength in the suburbs easily cancels out the Democrat strength in the city. Also large numbers of seniors too. In most other metro areas the Democrats rack up big enough margins in the city proper to cancel out GOP support in the suburbs/exurbs.
This is misleading - the city limits include the northern suburbs almost to the edge of the metro. There are far more urban areas outside the city limits to the east and to a lesser extent to the west. The urban parts of Phoenix are pretty Democratic.
One reason why Atlanta is stretching so far out is the lay of the land, incidentally - you leave the mountains open and build in the next valley instead.