Simple enough. A lot of the 57% stayed home and didn't vote because there was no real conservative to vote for. Romney was at best a moderate, lacked any real convictions or principles and generally failed to inspire us to believe that he really offered any difference from Obama.
This should be obvious to anyone who paid enough attention to note that Romney got several million fewer votes than McCain.
Until the Republican party starts putting up candidates that appeal to conservatives, they're going to keep losing.