E Pluribus Unum

It's partly because he'd have to campaign in front of the electorate he has, not the electorate he wished he had:

Does the American public care about the Nobel, a prize awarded by a bunch of ... foreigners? Wouldn't winning a "peace" prize brand Gore as weak on national security? Doesn't it show that he thinks he's better than us? Who would want to get a beer with a Nobel Peace Prize winner? Wait, did he just sigh?

It's also partly because he'd have to run in front of the political culture he has, not the political culture he wished he had:

If he entered the race, Gore would run headlong into the same dim-bulb, theatrics-obsessed political press that did him so much harm in the 2000 race. He'd also run into Hillary Clinton's political machine. He would own the climate change issue, so other candidates would have to start attacking him on it and distancing themselves from it. He'd be forced to spend his time discussing one piece of frenzied ephemera after another, instead of focusing on his animating passion. He'd end up in a bruising, demeaning battle, and winning some peace prize wouldn't shield him.

The process of electing a president, like so many things in the U.S. today, has become small and petty. It shrinks, cheapens, simplifies, and plasticizes those who take part in it, [as] Gore has already learned.

Fact is, Gore is smarter -- and already more powerful -- than the average politician-activist. He understands he can do more for his cause outside of this system than he could ever do from the inside. It's a rare individual who can say this. It is a rare individual who has the ability and potential to affect change on a global basis. Gore is that kind of person.

I think he believes that he can affect the kind of global change that is necessary -- without putting himself through the soul-destroying exercise that US politics has become. That's why I don't think he'll run.