Because they're idiots and need the money, if they plan it out beforehand, they won't need it. Don't spend extravegeantly as a rookie, sign an extension other teams can't offer, and then boom, sit out until you're traded. Not that hard to get an apartment vs a mansion.
NBA doesn't really have hold outs like the NFL does. you get fined heavily and suspended I believe, it's the same thing as the NFL where the player can just not play.
Minnesota will get something better for him because they're not up against him becoming a free agent where they have to take the best lowball deal out there...Teams will throw their best offers to Minnesota & they'll jump on the best one possible or suffer the consequences of getting worse offers as time goes on