This must be the role of polling played in it. At some point in the last decade (perhaps earlier), polls became a political weapon akin to propaganda. It's hard to grasp the change I try to write about, because it's a qualitative one and not just quantitative.
Sure, polls have always been used in that sense. But something vast changed in these elections: The Republicans believed in their own propaganda. In the past they may have pretended to believe that propaganda; this time they truly did.
Hence the stunned astonishment of Karl Rove, listening to the Ohio results, and hence the cheerful optimism of the Romneys and the Ryans all the way to the point when it was clear that Obama had won re-election. They expected to win and they had not planned for the alternative.
There's lots of evidence of this: Pundits confidently offered numbers based on assumptions about much greater Republican turnout and much reduced turnouts of young voters and African-American voters. But those assumptions were assumptions, hanging off pure air. So what made them so easily accepted as facts?
I'm not completely sure, but all this may have something to do with the ideological-bubbles phenomenon. If you belong to the conservative bubble, then you get your news interpreted by Fox News and by right-wing bloggers, and you get tweets which tell you that unskewedpolls.com is fixing all polls to look the way they should look.
Likewise, if you believe in a vast left-wing-media conspiracy, then all the polls the media reports must be biased, right?
These are just my thoughts and they may be wrong. But I think the cows have come home on some of the costs of the manufactured political wars and the self-segregation of politically motivated people into separate ideological camps. That most everything can be now seen through politically-colored spectacles is also part of the problem.