As far as why Sandoval isn't being courted:
1) Republicans are still trying to convince him to run for Senate
2) He's shown absolutely no interest in running for President
3) He's pro-choice (a treasonous position to the GOP Base)
Not really sure about why Bush > Kasich, aside from Bush's naturally high name recognition because of his last name and prominent role in the 2000 Election.
As IceSpear alluded to, Elizabeth Warren's desire not to run hasn't stopped liberals from trying to get her in the race. If you’re a big money donor, Sandoval is the person to trot out against Hillary Clinton. He's a young, pragmatic governor from a swing state who happens to be Hispanic. If the Supreme Court strikes down the ACA subsidies, Sandoval will look even better for putting his state ahead of partisanship. There’s a lot to like there, yet there’s been no buzz. We've had buzz for Walker, Romney and obviously Bush. Rubio is beginning to pickup steam. None for Sandoval, though. That blows my mind.
I think he has a lot of potential, but until he becomes a better public speaker I don't think he'll get far.
