I think what it comes down to is,
1. DL (and QS) are not willing to consider Trey Burke a sunk cost...not yet. They want him to at least have some value as an asset, and they're willing to let him try to improve that value as a starter.
2. Other teams are asking too much for the backup PG's they'd be willing to give up. They're playing a game of chicken with Utah because they think the Jazz are desperate.
3. Burks may be the "x" factor. Jazz only carried 2 PG's to start the season last year. Did they think Burks could be the 3rd if needed?
We could see a deal made before the season. But I think that depends on how other teams set up their rosters. Maybe Rozier and Hunter really impress for Boston and the Celtics decide to offload Bradley to give the youngsters playing time.