Because he hasn’t yet left office. The Bushes haven’t added substantially to their wealth because they were already wealthy.
Go ahead, show us. 
And no skewed Quinnipiac polls which oversample Republicans
http://www.realclearpolitics.com/epolls/2016/president/nc/north_carolina_carson_vs_clinton-5292.html
http://www.realclearpolitics.com/epolls/2016/president/nc/north_carolina_bush_vs_clinton-4173.html
I get all tingly when you talk like this!
Wow, North Carolina. Got the Alabama polls to show us too? 
Let me preface all of this by saying that I’m pretty damn ignorant about the Democratic presidential candidates. The Democratic race is so much less exciting than the Republican one, plus there haven’t been any opportunities to see the candidates debate yet.
Having said that, here is my ignorant impression of all the candidates running or featured in major polls:
Hillary Clinton - I was arguing about Clinton’s appeal with a friend the other day. He asked me if I trusted Clinton, and I said yes, in a certain sense. I think most people would agree that Clinton is, at the very least, rather secretive, and I sure would not trust her to tell me the whole truth about a situation. BUT … Hillary strikes me as the sort of person who would work tremendously hard to leave a legacy as not only the first woman president, but a good one. She’s not an idealist spouting policies that could never be implemented, and I don’t think she’d make any wildly unpopular decisions that might damage her legacy.
Bernie Sanders - I’m concerned about him, because from what I can gather, he wants to implement a lot more government services that need to be paid for, and we’re already in a mountain of debt. While I think things like free college tuition are great in theory, I’m not confident that they could be implemented without plunging us into severe debt (or else raising taxes to an insanely high amount).
Joe Biden - I’m counting him out purely for the fact that he keeps on going around telling the media that he’s not sure he’s ready to be president. (I forget his exact words, something about not being able to emotionally handle it or something?) Clearly he doesn’t want it that badly, and I’m concerned that if he were president he would fuck things up simply by not caring as much as he should.
Martin O’Malley - Not a fan of the way he apologized for saying “all lives matter.” My husband works in a county in Maryland, and I haven’t heard good things about O’Malley from my husband, either. And something about him just rubs me the wrong way. He strikes me as the sort of guy who would be super nice to you when he needed something from you, and then would toss you aside.
Jim Webb - I’m absolutely intrigued by the fact that this guy has so much military experience and wound up a Democrat. I certainly don’t know many military men who are Democrats. I don’t know a whole lot about him, but the idea of him appeals to me. Someone who has spent a large portion of his life around people with values that are different from his, and has been able to get along and move ahead in life.
Lincoln Chafee - His whole jump from Republican to Independent to Democrat irritates me, simply because if you look at his voting record, he’s always been a Democrat. If you’re a Democrat, just say you’re a Democrat. Don’t go playing games to try to set yourself apart.
So out of the prospective candidates, I’d want a Clinton-Webb ticket.
“Optimal” for winning or “optimal” for governing?
The message 538 seems to be expounding lately is that Sanders isn’t stealing any votes from Clinton, but if Biden jumps in he’ll take votes from the same pool as Clinton. So Biden could be a threat but if he’s going to run he’s taking his sweet time about it.
Booker (though he’s not running) and Sanders. I don’t think the country is quite ready for an open democratic socialist as POTUS, but it sure wouldn’t hurt to have one making speeches as VP for eight years.
Biden hasn’t been president yet. Senators’ speaking fees aren’t in the same galaxy as those of POTUSes. Particularly a POTUS who left office popular.
I know lots, but then I was in the military, and I’m a Democrat. I know lots of military Democrats, and even more military Republicans, but there are plenty of both. It’s really not that unusual.
He of course wouldn’t get as rich as the Clintons, but he could certainly have gotten as rich as Harry Reid. And Reid didn’t do it through speaking fees. He did it by being a very skilled investor, putting Warren Buffett to shame. Of course, it’s easy to be skilled when it’s legal to trade on inside information about what government plans to do. It was even legal until very recently.
Hillary, Sanders, Biden are all rather old. Even Elizabeth Warren, the juvenile in the group, will be 67 by the time of the Democratic Convention next year. There are five Presidents who were first inaugurated at age 63 or more; among these five, two died shortly after taking office, one had early symptoms of Alzheimer’s during his second term, and another, James Buchanan, is considered one of the worst Presidents ever. (The 5th of these old Presidents was George H.W. Bush.) And note that during the stresses of a campaign, an older person is more likely to suffer a health problem.
At the other extreme, the three youngest Presidents are all widely admired for their creativity and vigor: Teddy Roosevelt, JFK, Bill Clinton.
I really think the Democratic Party needs to nurture a younger candidate, and at least have him “warming up in the buullpen.” O’Malley?
Such candidates already exist, such as Cory Booker, and there are some prospects on the horizon(no, not the Castros. I don’t care how attractive or charismatic you are, you aren’t winning national office when you can’t win state office).
Jeb would probably disagree since he’s been whoring out ever since he left office:
“The Bush campaign voluntarily disclosed details about the candidate’s speaking and consulting fees to select reporters, telling Bloomberg News that he earned $1.3 million a year from failed investment banking titan Lehman Brothers, and $2 million a year from British banking giant Barclays. Both firms have been embroiled in scandal since the 2008 financial crisis, with Lehman filing for bankruptcy and Barclays pleading guilty to manipulating key interest rates and being fined by U.S. regulators for rigging energy markets. The Bush campaign also told reporters that Bush has reaped $9.9 million in speaking fees since leaving office.”
No such thing as being rich enough, apparently.
I think the optimal ticket is the one we are eventually going to see, which is either Sanders/Clinton or Clinton/Sanders. They are both of an age where this is realistically their last shot at the White House and they each have a powerful pull on a large block of voters (Sanders on people who want to see income inequality addressed and Clinton on people who want to see a woman in the White House) so I think what we will see happen is that one of them will win the primary and then recruit the other to run as their VP. The one who loses the primary will know that they no longer have a shot at ever being president in their lifetime and will swallow their pride and accept the VP nom.
The Castros are from Texas. It’s not like it’s a real state or anything.
JFK? Vigor, sure, but probably not the kind you mean. But creativity?
No. Absolutely zero chance of that happening. Clinton will pick a loyalist and Sanders will pick someone that won’t muddle his “authenticity” brand.
Don’t be too sure about Sanders. He’s been in the Senate long enough to know that he’s more of a mouthpiece for socialist ideas than a sea change.