Why in the world would they bet on Jeb Bush over Trump or Carson? Look at the actual polls, Bush is doing worse and worse, while Trump and Carson are rising: http://i.imgur.com/naxgnhi.png http://apps.washingtonpost.com/g/page/national/rise-of-the-a... (yesterday's numbers)
As the election approaches, the influence of insiders rises and Republicans especially are very obedient to authority figures. Historically, the candidate next in line according to Republican insiders always and without exception wins the nomination, even when he's very unpopular with the base. Therefore, analysts find Trump a very long shot.