I thought most of Cruz's followers were aged religious followers that tended to be highly educated. (ie. those that still have home phones). I imagine it is harder to poll those that don't have home phones (and change numbers every other year). Internet polling is a thing, but I imagine there is few older folks (college educated) that bother with doing them since they require you join these poll groups that dole you out rewards for filling them out.
That leave having to go door to door in some place that is not NYC with those unwashed rural dwellers. /s
The polls about Rand have been pretty accurate.