This makes sense from two perspectives -- one, if Gore's truly done with politics; the other, if he's secretly dying to get back into the thick of them.
Al Gore is enjoying the good life as a celebrity, environmentalist do-gooder and well-heeled businessman. He may simply have no desire to go back into the political shark tank -- and tarnish his own halo -- for either of two candidates who have no real claim on him.
Or, of course, he may be enjoying all the buzz about the possibility of his heading the ticket as the party's "savior" . . . and wondering just how many "legs" such an idea might have.