Why every team does it?:

Raptors:

Jalen Johnson has shown so far that he has potential to be a core piece in the future, and I believe he would gel well with Barnes. Although it's only been 15 games he's played good this season and he's out on a wrist injury, it may still be worth taking a risk on him. You could even delay this trade until February to see how he returns from the wrist injury.

Hawks:

They need to contend and Siakam would be a perfect fit in their current system.

Thunder:

They are contending and have a weakness of bench points, Bogdanovic solves this problem.