This might be a little bit of a bubble effect on your part. Jeb Bush absolutely has a chance to win the Republican nomination. He's not presumptive by any means but in a field of 16 or so, he's top three. That's why he's doing it. (And arrogance -- but everyone who would even consider running for national office has a certain mindset, and arrogance is part of the package.)
Could it be, is it possible, that he actually thinks he is the best candidate for the job? He has a father that ran the CIA and was a president, a brother that was a two term president and he is no-doubt well connected on the world stage. He was the governor of a major US state that has a major connection with foreign nations to the south and immigration. Strip away the fact that the majority of the country agrees that his brother did a crappy job and just look at his resume and pedigree and why wouldn't you run? Meriadoc. Edit: Meriadoc -the electorate has a very short term memory problem. If he's compelling enough in a debate and is more "likable" than Hillary (assuming that's his foe), then he has every bit a chance of winning as any other GOP candidate. Hell, Ted Kennedy KILLED SOMEONE and remained in power for decades. People conveniently forgot THAT, I think they can forget that he has a dullard of a brother.
I do think Jeb truly thinks he's a best candidate. I hate the fuck out of the man for plenty of reasons, but he's leaps and bounds better than any other current GOP candidate, and certainly better than his brother. However. I have to believe he and his team have to see the problems that he brother presents. Yeah, they electorate has a very short memory, but he brother is starting more and more to be recognized as the war criminal he is. And that's all well and good if he can separate himself from his brother, but this week he was in the news for saying he still would have invaded Iraq even knowing what we know now. That kind of thing is going to ruin him, among moderates, among the GOP electorate who dislikes W, among the media, and especially with the attacks the left can throw at him.
Bush arrogance is blue blooded, American dynastic arrogance that outstrips the Kennedys in ambition and questionable political maneuvers. Entitlement is a better word. He absolutely is a favorite but that speaks more to the Republican disarray than anyone actually wanting him to run.