First, let's establish the purpose for a license plate. A means of identifying a vehicle. So far, so good. A wild guess would be that each state having only 1 design instead of 11 would make the identification process a tad easier. If you want to make a personal statement, try a bumper sticker or license plate frame.
Some states have simple designs representative of their state.
They seem to have grasped that busy artwork is unlikely to translate well to a 12 inch by 6 inch piece of metal, often only glimpsed while hurtling past at 70 mph. Indiana's last license plate made me wince. Both because the tropical sunset look was misleading about a state whose northernmost section seems to get 37 days of sunshine a year, and because the colors clashed with so many paint jobs. For the current plate the State has wised up in terms of simplicity, although originality is still an issue. We now have an outline of the state.