They are so enclosed in an intellectual bubble excluding Unapproved Thoughts™ that they simply cannot fathom someone with Unapproved Thoughts™.
The Middle Class votes against Democrats in their own economic self-interest, for example. Yeah I know, math is hard. And seemingly Unapproved™ as well. And they're all smarter than you and me, too. They'll tell you, if you ask.
And this analysis completely ignores the way the Left is attacking employment (especially through EPA regulations on manufacturing) and applying the law inconsistently to benefit particular minority groups at the expense of the Middle Class.
Of course, it's so much easier to Leftie self-esteem to say that Kansas is full of racist dog-whistles than, you know, voters whose votes need to be earned.
More here on the Tea Party as the true party of the Proletariat and a Marxist analysis of the Progressive State.