Here's the problem... We don't get 12 weeks. We have some of the longer academies in my immediate area -- about 6 months, 26 weeks or so. And that's not full time DT training... that's covering everything that a rookie officer needs to know (in theory) when they hit the streets. Because, in hour 1 of day 1 of their field training, they can find themselves doing anything from talking to school kids to a life-or-death fight, under fire. So, over that academy session, they not only have to learn enough to fight -- but also things like how to search, how to handcuff, firearms, emergency vehicle operations, legal procedure, laws of arrest, elements of criminal offenses...
So, physical control tactics have to be things that function under high-pressure situations, be learned fairly easily, retained well, be scalable to the resistance encountered, meet legal standards and liability concerns, and more... Traditional martial arts training, wether BJJ (yes, BJJ IS traditional martial arts training) or something else, simply doesn't cut it. That's why there is literally no DT program that is purely a martial art.
I've never said that BJJ can't be of use, or has nothing to teach. But overemphasizing one range or one sort of fighting isn't acceptable, either. For a while, the Gracies pointed to a study of police use of force showing that most fights went to the ground... Yeah, but that was POLICE use of force. And they went to the ground for specific purposes -- to position a suspect to be cuffed, robbing them of a lot of their mobility and opportunities to escape by putting a freakin' planet in the way. If you end up in a submission hold or lock -- you have to be able to transition to cuffing, or the two of you are stuck there until someone rescues you. (Holds and locks aren't as reliable in the real world as some people might think, either, but that's another discussion...)