Why the Hawks do this? They are freeing up minutes for the number one overall pick Risacher, while simultaneously adding depth to other positions. This move allows them to potentially trade Capela on the last year of his deal. McBride is a great spark off the bench on a good deal. Robinson allows them to move Capela, or they can flip him for more assets. Dadiet is a young first round pick that they can develop.
Why the Hornets do this? They've been putting Richards in trade talks for a while now, with reports coming out that they'd accept two second round picks because they see Williams as their long-term center. Knicks pay their asking price.
Why the Heat does this? It is basically a free second round pick for them. They don't care about Burks. He doesn't play.
Why the Knicks do this? Thibs gets the apple of his eye, Alec Burks, to make up for the lost bench scoring with the departure of McBride. Knicks get a tall forward off the bench who can shoot and defend, which is something they desperately need. Hunter also unlocks a true 5-out lineup for them. Nick Richards is a big rim protector off the bench. Something they are lacking in the absence of Robinson. He allows KAT to shift over to the 4 in certain lineups, similar to how he played with Rudy in Minnesota. Bonus: They keep their only tradeable first, so they retain SOME flexibility.