Not just voter apathy, but voter discouragement. If districts were divided logically, Republicans wouldn't win many key areas through gerrymandering. Then there's manipulation of polling places in different ways to make voting more difficult or even frightening for some people to show up. A fair election doesn't work well for the GOP, so they make sure everything is done to help their results. And this time around they may be doing even more subtle things - see recent news of Steve Bannon's admission of having people in place to question voter authenticity. More scare tactics.