In PA, they have yearly inspections AND local and state police can stop you anytime if they see an obvious safety issue.
A couple years ago I was pulled over by a NJ state officer for a headlight being out while driving in NJ. No ticket issued. I think they were looking for a reason to pull me over. Might've been a slow night.
IMO, if a police officer stops behind a car at a traffic light and sees an obvious safety problem (bald tires, exhaust pipe hanging, overly tinted wheels, tires sticking out too much, etc.) I think that's a good thing for everyone. A lot can happen between yearly inspections, and there are also "sketchy" inspection stations that pass sketchy cars for their friends.