This article in the Boston Globe is a good wrap-up summary of the very basic ways in which the Romney campaign went so wrong… and the Obama campaign worked so well. Key paragraph informs us that Romney wasn't that into being President anyway.
More than being reticent, Romney was at first far from sold on a second presidential run. Haunted by his 2008 loss, he initially told his family he would not do it. While candidates often try to portray themselves as reluctant, Tagg insisted his father’s stance was genuine.
“He wanted to be president less than anyone I’ve met in my life. He had no desire to . . . run,” said Tagg, who worked with his mother, Ann, to persuade his father to seek the presidency. “If he could have found someone else to take his place . . . he would have been ecstatic to step aside. He is a very private person who loves his family deeply and wants to be with them, but he has deep faith in God and he loves his country, but he doesn’t love the attention.”…
Yeah. He realized that he might actually have to work, and he wouldn't be surrounded by yes-men.