My impression is that it is a combination of disenchantment with Roberts and a lack of knowledge about Orman.
While it is true that Roberts has become a Washington insider, he is a Washington insider with a conservative voting record. Not perfect, but darn good. His defeat would certainly please the NARAL, ACLU, Planned Parenthood, and the other progressive groups who have consistently found Roberts to be an opponent.
I don't get the idea that defeating Roberts would be a great way to punish the GOPe. A Roberts defeat would allow the moderates in the Republican Party to argue that Orman won because he attracted the middle of the political spectrum against the conservative Roberts. A Roberts' defeat would allow the GOPe types to point to Kansas as a perfect example of why you have to run a moderate squish in order to win.
Orman is painting himself as an independent and running "a plague on both your houses" campaign. And it could be resonating. People are fed up with career politicians treating re-election as a divine right. They're disgusted with both parties. Robert's past voting record reinforces just how long he's been in Washington. Orman's strategy may well pay off.