Hostile Higher Existences' Interference

After leaving that advice to the Phoenix Emperor and the royal families, Weiss left the royal palace with Alice and no one stopped him.

At least, the Phoenix Emperor knew that he couldn't stop Weiss since Weiss must have other things to do. If Weiss had accepted the engagement with Ivy, it would have been a lot easier for the Phoenix Emperor to bind Weiss to the Phoenix Empire.

However, the Phoenix Emperor knew that he couldn't bite off more than he could chew. For him, it was already a good outcome that Weiss wasn't hostile to the Phoenix Empire and at least was one of the Dukes of the Phoenix Empire.

So even if Weiss traveled to other nations, Weiss would still represent the Phoenix Empire since the rank of a Duke might not have political power, but they were protected by the Phoenix Empire.