Romney is smart but not likable. Why? He is uncomfortable in speech and somewhat nerdy. Charisma is a little ( a lot) light. He has changing positions.
Plus his money. There is enormous jealousy over wealth in this country. Not among all obviously but those in the middle ground.
Plus the media beats him up fairly well. I agreed with his criticism over the current administration handling and reaction to the Middle East rioting/murders. The media killed him on it.