Correction and retraction. Celtics did not trade Crowder. There was a deal being proposed, but it didn't happen. Which makes them trading Bradley for Morris even more weird. They've got like 15 forwards now.
I see the logic tbh
Bradley was going to be an UFA next summer, and they have guys (Jaylen, Terry, Marcus, Gordon) who they believe can play the two position, and where they were thin at was that 3, stretch 4 position with Kelly getting that Miami money. Crowder plays positions of need for the Cs (3, small ball 4) along with having the best contract in the league, so they would prefer to keep him over Avery.
So with guys that can play the two, along with the fact that they were going to lose Avery anyway next summer, it made sense to trade him. And they ended up with a player in Morris that not only fills a need, but is on a really good contract right now. I like it for the Cs.