More than half of the U.S. states have less than 5 million population. Moving violations and traffic tickets are usually administered on a state, county or local level. These aren't federal crimes, so it makes sense for each state to have their own unique system, as they often do.

In fact, as I write this it seems obvious that this system could be implemented without too much trouble in at least on U.S. state. Why wouldn't they jump at the additional revenue?