They might have just drafted him to be a good player on the team. If you want to develop other prospects on a D-League team, they need to have competent teammates. I'm not aware of the roster makeup, but if the team needed a good big, Ayres should be one of the better D-League big men, which would help us develop guards. It's not like every D-League move is based on eventually bringing them over, some could simply be just "we need players who can play on this team".