The answer is that the reporters are all upper middle class, and are looking for Republican class characteristics. When they don't find those characteristics in a Republican candidate, they don't report the discrepancy. At the same time, those reporters don't expect those characteristics from Democrats, so they take every possible interpretation to show how unauthentic the Democratic candidates are.
For a more complete description, go to the Daily Howler. Then look back at the earlier report of the same phenomenon.
It's a class thing with the reporters, and the reporters are NOT working class people.