Just because you have a choice between A or B doesn't make it free-market economics.
He can choose to play in the US, or he can choose to not play in the US. Those are his total range of options as far as the Spurs care. They don't give a damn if he's making $1 billion or $1 in Europe, if there's a probability he's going to wind up being another Oberto, that's the overriding factor into what they are willing to offer him.
It's a straightforward risk-benefit analysis, with the boundary contraints for the Spurs being:
-he won't sign at all
-he won't sign, they'll trade his rights and end up not getting value for him
-they'll sign him to a contract that way exceeds his NBA worth and be stuck with him
If not formally, I guarantee that the Spurs are at least informally placing weighting factors on all of these risks, with the primary factor being the third risk.
This is like have a discussion with a freshman who's just taken his first psychology course and now is trying to analyze everybody. What, did you just finish Economics 101 and are now trying to apply it to everything you see?