It has been that way at least since I started racing in 2007. Cat. 1 and those wanting to participate in a championship event are required to have an annual license. The one day license is the vehicle used to provide insurance coverage to racers not affiliated with USAC and is required for participation in USAC events. Even if you didn't explicitly pay for the one day license, it was probably included in your entry fee.
http://www.usacycling.org/buy-a-license.htm