Ranger
Yes, very normal for LE Officers not to have personal AR-15's. A few may have purchased one, but most officers would not purchase one.
You should also be aware there are 2 versions of the AR-15. One model is the civilian version of the Military M-16, and the other is the Vietnam era model with a collapsible stock and short barrel designated by the military as M-15 at that time.
Grillparzer
Sure, if the department provided one I wouldn't even have bought a handgun. Things like that cost money.
Erin
Some LEOs are issued some and are in trunk use. However I don't see why it would be any stranger for an LEO not to own one compared to a civilian.