It's possible, but in my experience the stats NHTSA looked at were compiled by the police department, not the court. (They cared about how many tickets we wrote, not how many convictions were obtained.)
A more likely explanation is the severe underfunding and understaffing of prosecutor's offices and state court systems. Most prosecuting attorneys are responsible for carrying hundreds of cases at a time-- they have no choice but to prioritize, aggressively.
