For one, he wanted the Star Supreme Elder to understand his own limits and recognise that the difference between him and the Pantheon still existed and would continue to do so. Secondly, the Star Empire was also important to the Pantheon, and it couldn't allow it to drift too close to the other superstates.
But that had its own limitations as well. The Pantheon wanted the Star Empire to follow its lead, but it never wanted to have it completely in its grasp either. After all, the Star Empire was already different from the other, more ordinary Tier 3 states around it. It could even be considered a semi-superstate in its own right. Because of that status, the Pantheon couldn't simply take it under its wing completely, as doing so would disrupt the balance among all seven superstates.
