Why are rigs only displaying one license plate?

This is technically violating my vow not to write any more letters to the editor, but the loophole, this is not a letter of opinion or view on a political topic or an issue effecting voters or taxpayers — it's a question.

Why are there so many rigs, (vehicles for you newcomers), driving around town displaying only a rear Idaho license plate? This state, along with most others, require displaying two plates, one on the front, one on the rear of the vehicle...