You are referring to an extra million votes as compared to McCain in 2008. I'd presume that a lot of whites stayed home in 2008 as well. What relatively little Romney did pick up as compared to McCain were whites who voted for Obama in 2008 and were teed off at him by 2012.
Neither McCain nor Romney could generate enough of a turnout from more conservative whites, because both of them were considered GOP establishment moderates, for lack of a better description.
The end results: McCain lost to Obama by about 7 points in 2008. Romney improved on McCain's performance a bit, but still lost by 3.8 points. (At least if you go by the released numbers, which undoubtedly overlook a lot of Dem fraud and cheating.)
Again, I suggest that you read Morris's book, at least the beginning. His formula for a Trump win this year was quite prescient. (You might say Morris atoned for his poor election prognostication in 2012.)
Just to review:
Bush ‘04: 62 million votes
McCain: 60 million votes
Romney: 61 million votes
Trump: 62.3 million and still counting