Maybe because he has a job waiting once Joe Torre retires.
Jon Heyman has this:
The Indians and Astros also have openings, and the Cleveland Plain Dealer identified Mattingly as one of at least five candidates currently being considered there. An outside opportunity could solidify his future in L.A., though it doesn't especially sound like it needs solidifying.
Mattingly said he believes Torre when he says he intends to make 2010 his last season managing the Dodgers. "He's not as leverage-the-media guy," Mattingly said. "But nobody knows the future." Mattingly understands the future isn't guaranteed to anyone. But his looks pretty secure in Dodger blue.
And the LA Times is in on it:
Mattingly, 48, is expected to draw the interest of the Indians and perhaps Astros.
Given what has been perceived as the "openness" of the Astros managerial search, saying that Don Mattingly is a candidate is akin to saying the Astros are looking for a hitting coach (they're not. Sean Berry is the hitting coach. Any Rudy J connections would be false, and Heyman's article says the Cubs are about to hire Jaramillo, anyway). Can you imagine the outrage from the Chronicle if the Astros hired someone from outside The Ten?