You'll see that in any/every state that gets snow, even those where it's illegal to not clean the roof of your vehicle.

People take their chances that they either won't be spotted by a cop or won't be stopped if they are.

I'm particularly fond of the ones that don't clean a huge layer of snow of the roof, then have to stop suddenly and the snow has melted on the bottom and slides forward, completely covering the windshield and totally obscuring the drivers view. That's just the best, especially in heavy traffic. /s