Because semi-autos in general suck. The lack of training by the police force - that is they can't hit stuff caused the need for high-capacity magazines. If they could shoot straight there would have been no need for the [bleep] semi-autos.
Never ever seen a down side to more ammo. Bill Allard was involved in more shootouts than anyone in NYPD history and it is sald that he never missed in a shout out and he ran in 1911 dry and his 12 guage with buckshot dry before stopping 2 felons.
More ammo is better than less
