But what is the purpose of an MRAP (for one example)?
In the incredibly rare event you have an active terrorist attack and can move the MRAP to it before it's over, it may provide the benefit of movable cover.
The rest of the time you have to park it (in two parking spaces likely), train people with it, fuel it, clean it, maintain it. It's just a huge distraction that sends a terrible message to the people you are supposedly serving.