Obama won because, while he isn't that good, the alternative is worse.
Most arguments made for Romney were actually arguments agaisnt Obama. Admit it, does anybody anywhere in any point in time ever knew exactly was were Romney's stances on anything? No; Romney was too inconsistent in his views in many major issues.
Related to that (get ready for some serious Looper style shit in this paragraph), Romney lost because he was basically running agaisnt himself. The Romney in the beginning of his campaign was not the same Romney at the end of his campaign. Thus, Past Romney essentially killed Future Romney, by way of changing his beliefs mid-campaign, thus Romney splitting himself into two separate quantic beings running against themselves-
The fact that Romney went out of its way to fuck Ron Paul and his followers in the ass ultimately destroyed him. He and his party (more on that in a moment) were not aware of the slow but steady demographic shift that has been happening in the last couple years. 11 percent of voters were black, 10 percent Latino, and 19 percent young voters.
By fucking Ron Paul and followers in the ass ultimately destroyed his appeal to the three tiers mentioned above. (Yes, Paul was popular with the above mentioned).
And finally, Romney lost because of the Republican Party. On the last couple years, the Republican Party went way far right for their own good. What once was the Party of personal responsability, laissez-faire and the triumph of Capitalism, ultimately turned into a bunch of theocrats forcing their Catholic values on everyone else, war-crazy PTSD-struck psychopaths, racists, and Glenn Beck.
Unless the Republican Party goes out of its way to reevaluate itself and glance of the mess it turned into, like the Democrats did in the 90's with Clinton, they may as well cease to exist.