The caucus system lends itself to this sort of thing. You don't just show up, cast a ballot and then leave. You need to hang around for a while. This means that casual voters (or people who work off-shift) do not attend.

On the Republican side the Evangelical wing has a much larger voice than they do in general elections (or daily life) which explains the last two winners and how Cruz has moved in front now. Still does not explain Trump.

Obama won Iowa in the general election in both 2008 and 2012 so the evangelical influence only goes so far.

btw, I would LOVE to not be first in the nomination process. What a pain in the arse. We get hit with so much crap so early and so often it turns ones stomach.