Remember this? Remember when Armin questioned why Erwin made this information public? Armin wondered if the commander had and different motive.And he did.
Erwin knew before everyone else that if Eren can turn into a titan,there are others with the same ability,seeing how the Colossal and Armored titan where clearly intelligent.
He also knew these people where in the trainee corps,and we wanted to make sure they where controlled and he could get them if necessary.He wanted to make sure they joined the Survey Corps so he told this information that would peek anyone’s interest,especially those of a titan shifter….
And it worked….
Bertoldt and Reiner where going to join the Military Police remember?Why do you think they joined the Survey Corps instead?