Because Repubs don't fight. They cringe and give in rather than be seen as "mean" and "evil." That's why the Dems win every long-term fight.
The Bush v. Gore situation in 2000 would be the big exception to the rule. Bush and his campaign did fight all the way to the SCOTUS to gain the White House.
On the other hand, the wimpiness of the Romney campaign in the face of an unprecedented degree of 'Rat election cheating and fraud last year is all too typical.