Because they're checking it's deployed correctly before letting people download it onto their own systems.
They also can't add patches earlier all the time because of the certification process which the console companies make them do.
@Turelus - EU PC Megaserver "Don't count on others for help. In the end each of us is in this alone. The survivors are those who know how to look out for themselves."
Some companies setup for such things, unsure of the cost on their end. Others do not. Zos cannot do it since they did not design to do it. The answer is that simple.