Because whether you like his current play or not, fact is he took way below market value at the time to play the Spurs specifically, and the Spurs alone. Trading him could arguably be considered a slap in the face, given the original terms of his signing, whether explicit or implicit. Now granted, that moral obligation has lessened with the mere passing of time, since he'd have played most his contract with the team he signed even if he's traded immediately. But point remains, the negative consequences from trading him concerning future free agency signings for a small market franchise that is not a traditionally a hot FA destination could potentially far outweigh the benefits. So, unless you can get something that is a significant improvement, we might be better off standing pat. And for the same reasons some here are so keen on ridding ourselves of him, it's unlikely franchises are lining up with offers. So though you might wish what you please, I wouldn't hold my breath waiting for anything to happen.