The democrats offered nothing and got nothing in return.
Perhaps if they offered something to people, like maybe reforming the healthcare system that will bankrupt you for a bandaid, I wonder if some of those nonvoters would have paid more attention.
I just don't think that's the end all be all answer to your argument. It's not as data driven as you might think. There is much more working under the hood then just shifting votes around.
Votes aren't solely made on ideological basis. If I think there is a subset not participating but they would under the right circumstances they wouldn't be a part of the calculation, either..