Reasons for doing it:

Thunder- The Thunder are the best team in the NBA, and they add to that with the addition of Cam Johnson. He is a great shooter, while being a decent defender and rebounder. They give up 2 of their many firsts, and one of their former first round picks from this past draft in Dillon Jones, aswell as 2022 FRP Ousmane Dieng who is more than likely not going to pan out to much. It's not too steep of a price, and it is worth it as this increases their title chances even more.

Nets- Obviously the Nets are tanking right now, so getting 2 firsts and a couple young players is a good haul for Cam Johnson, who is one of their best players. They also get good role player Kenrich Williams who might be worth an asset or 2.