I think the issue relative to past practice is that many states have passed Voter ID laws, and a state driver license typically serves as acceptable ID for that purpose. Therefore state driver licensing agencies have been under pressure to limit driver licenses to residents. It really doesn't make a tremendous amount of logical sense, given that many foreign, permanent US residents aren't eligible to vote but are eligible for driver licenses... But it's seen by most as better than a national ID card that inevitably would put your whole life under Federal Government tracking and control.