Allowing the Defcon/Threat Level changes twice per day to eliminate the update penalty. Many players cannot be on at update due to their timezones. Those that can, change their Defcon/Threat Level before the update, collect taxes after the update, and change the Defcon/Threat back after the update. Players that can't be on at update are forced to collect less in the way of taxes or expose their nations to potential attacks leaving themselves at a disadvantage to other players who are on at update.
Spy attacks should still freeze Defcon/Threat Levels for a day.