Why no more smiles?

I had to renew my driver's license and photo yesterday. And for the first time ever I was told NOT to smile for the new photo. I know that the passport photos must be expressionless (although they look so sad, glum, and strange that it seems strange to call them expression-less) but why?

Why is it that a smile is no longer allowed? Do people not smile when going through customs? Or when talking to the police? Can the police not figure out how you'd look frowning, crying, or angered if your photo shows you smiling? The new photos make you look so guilty. Like a mug shot. Not as the happy traveler driving around, or visiting another country. What's next? Will we be asked to "step away from the vehicle with your hands where I can see them, and NO SMILING!"

No longer will I be happy to show my ID (not that I've been carded in years) - but still, showing the photo used to be something to feel good about - not anymore!  

And the old photo was so cute - I was a lot younger back then - my clothing chic, my haircut stylish, my makeup carefully applied, and my smile radiant. I was not even allowed to keep it - I suppose they have special ways of disposing of expired licenses. But I miss seeing that photo in the viewing window of my wallet. Of keeping it in a memory box to cherish always (like my old video card, student ID, and Science World membership - all showing such happy smiles and linked to so many happy memories.)

Oh well. I suppose the government just wants to remind us of who's in control and how serious it is to be legally entitled to travel.