Why? He's unrestricted, it means you have no control over the situation. Maybe he stays, maybe he goes, if he's unhappy he's gone (and he has the potential to be looking to build his brand). Durant is under contract, he has to both be unhappy, and you have to agree to move him. Durant doesn't have the same incentives as Brown either, so if you put a good team around him, based on his history he probably hangs around.
People assuming Jaylen is just a lock to come back and play #2 to Tatum in 2 years as a UFA are probably looking through green tinted glasses a bit. Sure he COULD return, and maybe he will, but there are a lot of variables that you can't control there, and the few indications we have of his plans indicate a guy looking to build his brand... and #2 guys don't have the brand equity of #1 guys (especially if they were never #1 guys).
Edit- In any analysis of Jaylen we should be going in looking at 2 years, because anything past that is basically a mystery, and none of us know anywhere near enough about him to know what he'll do... even he probably doesn't know what his preference is yet.