Of course more guns are part of the answer, probably most of it. I’d also argue that police are generally useless in preventing crime, and don’t have much impact at all. That’s not their role. They’re for the protection of the government and for arresting people after a crime has been committed. And they also generate revenue although in most places not enough to pay their keep.
Police are there to arrest people after the fact, to put people in Jail, enforce probation, do all the things the criminal justice system needs enforcers for.
John Lott’s research shows that the Criminal Justice sytem, as a whole, deters crime about as much as armed citizens do.
In fact, the two reinforce and support each other (in a sane society, which is still most of the U.S.)