IMPress Polly despite what you may think, this isn't rocket science. Obama received 10 million fewer votes this time than he got in 2008 . . . and so people were not pleased with his first term performance. Romney received 3 million fewer votes than McCain received in 2008, and so in the eyes of low information voters he was not enough different from Obama for them to vote for him instead.
Low information voters put Obama into office in 2008 because they believed all the over the top press hype about Obama. Low information voters returned Obama to office in 2012 because they were not intelligent enough to understand the real differences between Obama and Romney.
Now you know.