Good question. The answer of the police/courts is probably that they protect the public at large by protecting the system of law, but that takes the form of mere apprehension of perps after the fact. They don't have to physically stick their neck out to protect anyone, see eg. Uvalde cops cleared of wrongdoing for standing by while an active shooter went around executing kids.

The legal system is happy with this because law and procedure have been decoupled from any moral framework, freeing up the cops to act as low liability armed guards for #currentthing.