Why not though? Too many question marks around Exum. Will he retain his quickness after the injury? Will it affect his desperately needed confidence? Will he be able to develop a decent offensive game? Will he be good enough within a reasonable time-frame to compete while the team still has its core?
With Schroeder, you get one of the best young PGs in the league who can already produce at a high level. He can probably be signed for a reasonable amount of money, and it makes sense for Atlanta since they can take their time developing Exum behind Teague.