Then, up to maybe the early 70s, policemen wear shorts. Now they wear pants.
Wearing shorts seem a better idea; maybe they can run faster. At least that is what they tell us during PE class. Maybe if policemen can actually run faster with shorts, there'll be less crime because they'll have better chance at chasing criminals.
Wearing shorts also cut costs - good for the budget. So less hot, again less air-con / cool drinks so again less cost.