Just my own observations....
By way of introduction, I'm a Federal lawman. (Go figure...) I have a good number of LEO acquaintences from the twenty-five years I've been doing this.
Generally speaking, regular officers in most law enforcement fields are either pro-second amendment or at worst, neutral. They would like to prevent criminals from getting guns (duh!) but are not worried about normal citizens.
However, "Administrators" are usually anti-gun. Normally the bigger city types who, as clubsoda22 mentioned, are appointed by mayors or city councils. Very political position. From this, it follows that those who want to be promoted into command level positions must in some measure "suck up" to the boss or bosses; therefore, anti gun.
As time goes on, I've also noticed that new LEOs are not shooters like the old timers were. So the whole field may be changing. I sometimes wonder if hiring practises, profiles and "affirmative action" helps this trend? That's a can of worms for another time.