I do not understand this logic whatsoever. If you're a rebuilding team like Arizona, Upton would be the first guy I'd build around. Young, high ceiling, relatively cheap long-term contract extension given that he might become.
If someone offers them a baseball equivalent of Herschel Walker where you get a top of the rotation pitcher, a high level position player and a solid bullpen piece or back of the rotation starter, you have to at least look at it. Royals offer them Greinke plus something else, hey, it is a possibility. Odds of it happening are probably low single digits though.