I would guess ego and curiosity are there. If you are having such success at one level it is natural to look at the next one up. I doubt $ had too much to do.
What makes me wonder is the Willie Lyles issue with the Ducks. If they are facing probabtion what better time to do a Pete Carroll?

He hasn't won a nc, that's why he declined.

Probably just wants to stay in good standing amongst owners in case he ever decides to take the next step.

I don't blame Kelly for thinking about making a jump to the NFL level. Personally, I don't think he would make a good NFL coach. His offense is too gimicky. The speed and talent level in the NFL would largely neutrallize the gimicky facets of his game. Sure, it's appealing, especially to teams that aren't doing well and especially on offense. He might have some early success as the element of surprise would take hold, but I do not think it would last. JMHO. Also, I think his stock may be declining as he has either spurned the NFL twice or been rejected, or whatever it is. People may not take him as seriously. As for Oregon winning a national championship, absolutely possible, so long as they don't meet the SEC Champ. They have met the SEC champ twice and that offense was neutralized both times and they lost. But Oregon gave an SEC school the toughest championship game any of us have had in the BCS era. Of course, that was Auburn in 2010.