It's baffling until you consider the effect of culture wars, or 'wedge issues.'

Economics is complex, I mean look at this thread alone on HN (and we're well above the average in education and intelligence). Abortion, religion, and other controversial topics, however, are far simpler to understand. The Republicans know how to get votes through that mechanism of holding tight to certain ideological components of their traditional voter base.

Another large part of the base are 'small government' types, less interested in economic problems and more interested in individual freedom.

I think that's a rough answer to your bafflement.