Car Rental Economics

I saw this banner ad today, and it brought back a fond memory from college:

Senior year, a friend of mine and his now-wife wanted to come down and visit during the Christmas break.  He owned no car, and hers was old enough as to be not entirely reliable enough for a 300-mile trip; so naturally they looked into renting.  This was the mid-90's, so we found a copy of the Yellow Pages and started dialing rental companies.  We soon discovered - much to our surprise - that no one rented cars to people under the age of 25.

After a brief period of near-despair, one of us thought to check with U-Haul.  Inexplicably, they rented trucks to anyone with a license!  I believe we went on to pit Ryder and U-Haul against one another in a bidding war over the phone, and the final price wound up being lower than any car would've been.

Upon arriving at my house that winter, my friends proudly raised the rear door of the truck and displayed the entirety of their cargo:  A huge Taro Root, secured to the floor with a long strip of duct tape.  Their luggage had been stowed in the spacious cabin with them.

I'd always assumed that the over-25 rule was based on some esoteric actuarial calculations, and I assume now that the risks of renting to a 20-year-old can't have changed substantially in the time since I graduated.  I'd be curious to know what has changed.  Is it just a mounting desperation to rent to somebody - ANYBODY - who will put up a credit card and a license?  Are 16-year-olds next?