You outbid all 29 other GMs for the guy's services. No one else wanted him at that particular price. Now you want one of them to take him off your hands, without any additional concessions from you? You paid market rate for a player, for which you sacrificed no players in return. Now you want a fellow GM to give you players, for that same contract? You trade a player in his first year. Then you ask future free agents to commit to you without a no-trade clause, and expect them to listen?For all these reasons, I agree, trades of this sort can be expected to be rare.