Unless it was at a light and you were directly opposite then for a time, cops looking at the windshield then the rear plate on every car without a front plate would be outrageously difficult while driving, and dangerous frankly as they would be taking focus off the road.

But the method isn’t 100% it’s just better than having a bad sticker, and works majority of the time. It’s all about it working often enough to pay for the ticket. My truck needs ~400 in cosmetic parts that are classified safety (cracked lights that still work) add in $60 for the inspection, I could get 3 tickets and still be under the cost to fix. I’ve gone 2 years without a ticket on my 2019 inspection, so I’ve saved $120 for the inspection and 400 on the fix. If I got the $160 or whatever ticket tomorrow I’m still net 360 positive. I can keep that trend of being positive going till it’s time to trade in, and get a car with a new sticker from the dealer.