I worked for U-Haul for years in the late 90s and early 00s. At one point the fleet's registrations were divided across every state in which they operated (unsure about Canada). But each state had different requirements for registrations, and sometimes a truck would be gone by the time the new registration arrived at a location. So that registration had to be sent back to headquarters in Arizona, and they had to anticipate where the truck would be so they could send the registration. It was not uncommon to have trucks 6+ months out of registration.

In 98, I think it was, U-Haul made a deal with Arizona, which has permanent plates, paperwork, and no registration sticker. Their entire fleet would be registered in Arizona, and U-Haul would pay a fee to every other state in lieu of registration there. This alleviates the need to get plates/stickers to a location to meet a truck.

Yes, we could have grounded trucks with expired plates, but I bet you have never been threatened, attacked, stalked, because you were unable to rent a truck to someone because it only had a fucking expired plate. I have, I know others who have.