Jazz is doing this because the Rudy-Mitchell duo is not working. The Jazz Chemistry is below average and they need to replace Rudy because he is not utilized in the Jazz systemm. Jazz trading for a veteran and a lob threat center is perfect because Jazz thrive in small ball lineups.

Celtics do this so they can upgrade their defense. Imagine having the best defense in the NBA with the Best defensive center & shot blocker. Celtics can utilize Gobert at their defensive end.