Reason For Each Team To Do This:
GSW: They have a serious lack of consistent scoring outside of Steph and Jimmy, and they get a young wing who is a more consistent scorer and a better shooter than Kuminga and probably would get the right amount of minutes in Mathurin. Their overall athleticism is also increased with the addition of Toppin, who can get easy lobs from Steph and Butler. I don't think they hesitate to do this, despite the draft capital given up.
IND: They have already stated that they're probably not going to offer Mathurin the money he wants in the offseason, so they get off him, and they get a superb upgrade at center in Nic Claxton. He is the perfect shot-blocking, athletic big that the Pacers need when Hali returns from injury. He will help them compete again next year.
BKN: They take a flier on Kuminga and try to develop him to the best of their ability. Kuminga also gets what he wants and takes 20+ shots a night. They also get a pick swap with GSW in this upcoming draft which they get to choose whether or not they wish to do so.