Reasoning
I had originally had Smart sent to Miami, but in this scenario, I believe this was a better value for the wizards, since Rozier would've been included plus taking the extra 6 mill from his contract. Wizards get draft capital in return and receive a center who is a few years younger than Holmes and cheaper freeing up cap space allowing their young guys to play more. Wizards are also salary dumping in order to make this happen.
With Horford either signing elsewhere or might retire, celtics receive a big that can shoot and fulfill the role of Horford and tingus pingus by achieving the same formula they once had, while also freeing up some cap space. Since bucks are receiving extra money, a pick is sent for compensation.
Bulls have now a younger core and adding Kuzma plus a center who is a few years younger than Vuc is a fresh start in their new era while building around Coby, Buzelis, and possibly Giddey if he stays. They also have a bunch of first which they can add onto their core or later trade for in a star.
Miami receives Kispert who's younger and has 4 years on his contract can be good value for the heat in the long run. With Duncan gone, Miami is missing a catch and shoot type of player, and he can fill that void. As I mentioned earlier, he has 4 years on his contract and over time you can build his value. If they heat decide to trade him later on for a star as a trade package at some point or extend him.
Bucks are disappointed in Kuzma performance and decided to go in a different direction who can provide better offensive power in Simons. He has a year left in his contract so they can test and see if he works in their system and could resign him cheaper after his contract expires or flip him at the deadline. Earlier I thought of adding smart who can provide defense initiating their offense not really looking to score. The one thing I think is a flaw of the trade for the bucks is while adding Simons, Porter Jr has stepped into a bigger role of scoring since Lillard is gone and has done well for them. And adding Simons would take his spotlight since he's a ball dominant guard. Plus he cost more. But overall, I don't think it's a bad trade for them if they decide to go into this direction.