That's because you believe Obama is some far left wing liberal which is not at all who he has been as president.
What color is the sky on your planet?
Cons have painted him that way, but it's really never been true of him. Sure, he's left of center, but outside of Obamacare nothing he has done has really been way out there. Politically, it would be a smart move. If Republicans confirm him, then he assures that the court is not given another very conservative justice should the Republicans win the White House. If Republicans refuse to confirm him, then it really becomes a huge political issue that Dems can use against Senate Republicans running for re-election. Republicans have long underestimated Obama's political prowess. Doing so again would be extremely foolish.
Other than Fascist Care, attacks on civil rights, particularly freedom of religion, promotion of gay marriage, fostering racial hatred, appointing radical left judges like Kagan, kow towing to hostile foreign powers including paving the way for an Iranian "ObamaNuke," while declaring that America is nothing special, there is nothing radical left about Obutthole.
You know, other than that...