Because Romney was not a great candidate in the context of today's Republican Party, but he was probably the best candidate that could have been fielded of those willing to run. I mean in the Republican Party of 1988 or 2000 or even 2008 he might have been a slam dunk because he could have touted his moderation and record more and earlier and been more consistent in his statements.
He also ran a pretty bad campaign. I mean Romney, as he governed in Massachusetts, could probably have pretty easily beaten Obama, but he couldn't run as that Romney so he had to shape shift into a "severe conservative" and disavow almost every position he had formerly taken in his political career or any public statement to mollify the Tea Partiers and other reactionaries in the Republican party. Then he had to tack back to being a moderate in the debates and in front of less strongly conservative audiences. He also didn't do the shape shifting very well in this day and age of video everywhere and the internet.
He was probably overly vague on far too much policy that matters to people so they couldn't trust what he really might do. It made it seem like he might be hiding a really reactionary agenda, which fired up the Dems to some extent. As far as foreign policy he either made faux pas overseas or acted like he just didn't care about foreign policy very much.
Lastly, I think he didn't take any strong stands on the craziest pronouncements of several Republican candidates. If he had disavowed some of the crazy rape and abortion statements made by Republican candidates he might have brought back a lot off the women's vote and been seen as a reasonable Republican which could have gone far in garnering their vote.
I think that in general the electorate won't forget nor put up with a candidate that constantly shifts his position to any circumstance and if Romney has any real convictions (I'm sure he does in his family and religious life and the overwhelming conviction in his business life seems to be profit possibly at any cost) as far as public policy goes. If he does the only one I could discern was that Romney should be President. My big question is whether or not he was "Lying for the Lord" as Mormon's are alleged to do (by other Mormons and ex-Mormons) or not. This is a well known tactic/policy so look it up -
http://www.exmormon.org/lying.htm
To some extent I think the electorate realized how deep a hole Obama was handed when he took office and understood that we actually have come quite far from where we were in 2009 and early 2010 and they feel that better times are ahead now. Enough people remembered what it was like under Bush and saw the Republican obstructionism in the Senate the day after the inauguration and in the House in 2010 and didn't like that and didn't want to reward it. I think they credited Obama for the calm steady stewardship of the country and economy (and were reminded of that in how he handled Sandy) and were willing to stay the course rather than go back to many of the policies that Bush followed that may have gotten us into the Great Recession of 2007. That's just my take.
Why did Obama win?
