Missing Plates

Why is it that so many cars in Las Vegas lack license plates? This is something I've been noticing more and more. Every day, I see several cars here without them, at least 2% of all the cars on the road. Maybe it has something to do with this. Before I moved out here, I had a car with a license plate clearly displayed in the rear window for a few weeks, and I was pulled over for it. Since I had a good excuse, and since the plate was clearly displayed, I was able ot talk my way out of it pretty easily. I just don't understand how people with no plates are getting away with it.