I had the same question shortly after the election.
See here.
I think best answer is that Obama failed to hit the same percentage of whites that Kerry had. Bush won Florida whites 57-42, while Romney won them 61-37. The difference for the state was that it has become less white and Obama won the minority vote by a considerably bigger margin than Kerry did. Obviously, Obama won blacks by a bigger margin than Kerry and with a higher turnout. The big difference was that Bush had
won Latinos in the state 56-44, but Obama won that vote in 2012 60-39 with a higher turnout.
Volusia County is considerably whiter than the state as a whole. I think it basically comes down to the racial swings. Whites swung to Romney and Latinos swung to Obama. In a heavily white county, I think it's obvious which swing wins out.