I know back home, the PD has a mixture of GSDs, Mals, and I believe they JUST got a dutchie. GSDs still dominant the K9 force back home. Also I've seen more GSD military dogs than I've seen dutchies or Mals. I know a lot of what you're seeing is departments deciding they want the lighter more healthy mals while other departments will spend the time to search for healthy GSDs with solid hips. Out here I've seen mostly GSDs as K9s. I think there is ONE mal on the force here but I cant be sure. I know a lot of the MWDs are bred in a breeding program that belongs solely to the air force but they will seek outside dogs as well.
Its really a matter of where you are and what the departments/handlers themselves prefer working with.