Pennsylvania has concealed carry and Philadelphia lost their case in the Penn. Supreme Court over 4 years ago. Any Penn. permit is valid in Philadelphia. Penn. even allows out of state permits.
There are just 8 states in the country without shall issue concealed carry permits or no permit needed at all and local firearms law preemption.
So you've noticed this happening disproportionately in those 8 states?
There's another factor that correlates much more to the locations of these incidences and it's not gun laws.