Yo,
GSW desperately needs space. A shooting big would open up the floor. Then, there would be a better access to the paint.
So, not a few options on the market. WC jr ? Cant be trade. Lopez ? To old. Zach Collins ? Not enough good defender. Turner ? Pacers wont trade him with Siakam in.
So, Stewart makes sens. For GSW, a shooting big with better potential. Also able to defend bigs and switch at least on to forwards. Also, they let go Kuminga for it, which seems a lot. But they get 2 future draft picks to include in an other blackbuster trade.
For Detroit, u get on pick to get a future young prospect that would fit better with their timeline. You also get a young one in Ziaire as a development bet. You also get Shrodder as a 6 man to set up plays and order this young team. If not enough for some people, GSW could also let go a guy like Lindy or Santos, Forwards who can shoot and defend.
For BKN ? They seemed to be interested in Kuminga and to be willing to give up picks. So there it is. They only let go a young prospect that hasnt yet be able to prove anything, and a veteran guy.