Some of the bad guys are both better trained

and more willing to shoot than the cops.  Or most CCW folks.
The first thing that the researchers learned is that our assumptions about criminals not training are wrong.  Nearly 40% of the criminal attackers in this study had received FORMAL firearms training (mostly in the military).  More than 80% of the criminal attackers regularly practiced with their firearms, with an average number of 23 Practice Sessions Per Year!  They conducted these practice sessions in trash dumps, wooded areas, back yards and “street corners in known drug trafficking areas”.  What that means is that the practice sessions were taking place in realistic environments, under conditions similar to those the attackers were likely to face in combat.
Some good information here