Because the card that came with it said it required validation by presenting a DL. It refers to finding a 24/7 location to do this, but many of the urban ones are unmanned and the website is not particularly helpful in indicating which locations are manned and which ones are not. If I could take care of this by visiting a desk at an airport, that would tend to be more convenient for me as I have a number of upcoming trips where I will be passing through to pick up a car over the next several weeks.
Interesting. I don't remember having to do that, but I got my card several years ago.