Well, really, the Kings were trading for 2 draft picks. Players have to move to make that happen.
However, he's not doing too bad for a rookie player with only about 21 mpg. 8+ ppg isn't too bad, but he needs to improve his shooting. #240 in PER isn't going to do him any favors either, and I think his job just got tougher on a Sacramento team that's no longer going to have Cousins.
Well, yes and no. A second round draft pick doesn't have great value in the NBA. Half of those guys end up playing their first years outside of the U.S.
Mostly, SAC wanted to get something for Cousins before he signed elsewhere. They ended up with five two guards, including Buddy who was a pretty high draft pick last spring and they got a first round pick, just in case they have to trade their first this year, which has some sort of conditional possibility of going due to a previous trade.
Mostly, Cousins was a bit of a malcontent who wasn't going to resign with SAC. Unless the Kings trade him, he isn't likely to be out of there, anytime soon. I believe he signed for four years, so he'll be there at SAC discretion until at least spring of 2020.
This is an opportunity for Buddy to make himself into a quality NBA guy. He's going to get minutes. But he's a hard worker, and will keep improving. He's got some room for that. He did look good in the futures game for All Star weekend.