Trae Young has only appeared in 10 games this season, and there's a good chance he doesn't appear in too many more. Per The Athletic's Joshua Robbins (subscription required), Washington's plan in the aftermath of this move "isn’t for Young to help them this season," instead allowing him to rehab from his injuries and not rush back. That doesn't mean he's done for the year, but it does hint that his injury issues may take some time to recover.
A team like the Wizards, who need to stack losses in an effort to keep their draft pick next summer, can afford to add a player like that.