User blog comment:SSWerty/Dragon Ball ST/@comment-120.28.64.74-20101201123915/@comment-1668079-20101203030358

Dark Kai can create universe, so if he had the chance he would just make a new one over the top of the other one. That kills all existing life and means that Dark Trunks would be instantly killed. Also, there is only one universe. Even if Dark Trunks can destroy 10 universe in one go, that's not a very useful power as there is only one universe at a time.