The servers being locked or not seem to be varying and/or rotating. Just a wild guess with no evidence to support it but I think maybe they are temp-locking some servers just to try to steer new characters to some that may not be getting as much traffic. I was trying to make a character on Ultros earlier and it was locked, I went and got a drink and threw a load of laundry in the washer then refreshed the server list and Ultros was back up and available. I just imagine some guy sitting at SE HQ saying "lock Ultros, Excalibur, and these other servers for 10 minutes so we can get some people to join Goblin and Leviathan".