Actually, the Spurs could have had Scola but they chose Splitter instead.
That was the calculus, pure and simple.
Splitter messed up the plan by delaying his journey to SA by a year (the team had factored a one year delay, not two).
If you look at the timing, the Spurs drafting Splitter and giving up on Scola was within a very short period of time that championship summer (at least that's the way I remember it, and I'm too lazy to look it up to confirm).
But my clear recollection at the time
was that the Spurs concluded that Scola was a demanding prima donna and they cast their lot with Splitter.