From the official Pirates of the Burning Sea site:
"When Pirates of the Burning Sea launched on January 22nd, we introduced our customers to 11 new game servers. Through feedback from our players and evaluation of our server populations, it has become clear that key game features require populations of higher density in order to function at optimum levels. When you take into account both the disparity in player time zones and the delayed launch of our title in some countries, we were spreading our overall population too thin. Also, in more recent builds, we were able to improve our server technology to allow for an even larger population than we were originally equipped to handle.
Providing our customers with the best game play experience is our first priority. Condensing our populations will lead to a richer, more vibrant game play experience for all involved, and our customers whole-heartedly agree. The character transfer option will not be available to our Australian customers on the Invincible server."