More people voted for the R candidate when Romney ran (2012) than when McCain ran. The facts (numbers) don’t bear out the false narrative that conservatives stayed home to protest anything. More votes than the last presidential election (2008) would tend to belie the idea as presented.
As an aside, Obama’s numbers went down from the 2008 election (when he ran against McCain).
I don’t have all the numbers, but I think we did see a lower turnout that projected. Additionally, Romney won the independent vote which McCain did not, so he picked up votes in some areas and not others. There definitely wasn’t the turnout needed from base voters to win. The left got their voters out much more than expected; ours less. I don’t think there was a massive conservative non-vote, but definitely some. I think most engaged conservatives were chomping at the bit to vote Obama out. There were likely some categories...Ron Paul types, certain religious leanings, etc that stayed home for a variety of reasons. If there was a massive turnout from conservatives of all stripes, the election would have looked a lot different. If not a victory, certain a narrow loss vs. the significant margin we saw.