I suspect in the new era the Spurs are entering, they are about to value cap flexibility the most bc they will need that third banana from FA either this season or the next and they don't have assets to trade for another player or into the draft lottery that they can spare. (I mean all these trade ideas are floating around for Mills, Diaw, Danny, Tony, Anderson, practically everyone we have guaranteed outside of LMA and Kawhi, but we don't have an indication that they will even move Boris, and some of these guys are too old to be too valuable and others too young and unproven, and I am sure Spurs would rather not trade Danny, the one asset that could really interest some teams, so I am assuming the guaranteed guys stay put).
Therefore, FA is the only way to get significantly better right now and thus they can't tie their cap with projects which at this point Bertans still is + he's risky bc of his injury history.