i think its fine the way it is and fly carpin provided a good researched answer to why that is most likely the main reason. however, i completely disagree with those arguing against lycan's proposal based on it would be a PITA to remember when your license expires for for the GNF to have to check for 365 different dates. that's how our driver's licenses work. and they expire like every 5 years and most everyone remembers to renew on time and law enforcement doesn't struggle with enforcement. whether you are the license holder or the law enforcement officer, if you can't read a license and look at the "expires on:" date, you've got a problem.
Your driver's license always expires on your birthday. That's what helps in that scenario.