The major parties are acting as if voter disutility functions are quadratic, meaning each party has to please the more vocal elements of its base, rather than cultivate the median voters. I'm not clever enough to see the strategy by which a limited government party could attract members of both the fiscal Leave Us Alone coalition and the social Leave Us Alone coalition.Now comes Voluntary Xchange, arguing in "Utah Has No Political Middle" that the notion of a median voter as we understand it might not work so well where voter preferences are bimodal. That appears to be the case in Utah. The national preferences appear, still, to be not too far at variance from Hotelling's uniform-on-a-line, but if voter disutility functions are quadratic, party polarization follows.
THE PRINCIPLE OF MAXIMUM DIFFERENTIATION.
That may be the simplest explanation for the political parties catering to the truest believers.