It's not a wrong decision by the Spurs. It's honestly good and better for the team in the long-run. There's no point in keeping a player that isn't interested anymore to play for the team. Kawhi loves that trades. Just too bad for DeRozan as he truly loves the city of Toronto Raptors and that trade really surprised him.
Leonard is a special player, while DeRozan is good but inconsistent, this is one of the big mistake the Spurs made in their franchise.
If they have traded Leonard to someone else, a star of course, Spurs might still has a good chance to be in the playoff spot now.
It's unfair to just point it out to DeRozan why Spurs will not make it into playoffs.
We can obviously see that the team is really struggling this season. The competition in the West is also tough.