Why did I get a letter saying I needed more identification for my passport application?

This is not terribly unusual. sometimes another person with the same name and birth date already has a passport , so they need more info to identify you. sometimes someone has stolen your social security number and gotten a passport...identity theft...so they need to know who is rally YOU. Another reason is that you used a driver's permit not a license. Any time someone uses a permit or a license that is less than 6 months old, they ask for more info. This is due to the problems they have of people using stolen or false I.D.'s