If I had to guess, since the police already ignore those tinted plate covers (which triggers another whole rant from me...) probably to hide it from any officers who might care to question this wildly illegal plate. Not saying it makes sense....

People respond to seeing things that are out of place. A cop seeing that plate is likely to do s double take and, so, it attracts police attention

Having a tinted cover ALSO attracts police attention but it's a lot more common and a lesser violation so it's more likely to be overlooked