Confer a kingship?
In the Supreme Court Imperial Dynasty, the conditions for conferring a kingship are very harsh.
It's not that when princes reach the age to start a family, the Emperor would simply grant them a large fief, and then they become the king of that territory.
Even for princes, they must at least have reached the King-Level Realm, or rule over the territory of more than four nations, before they are truly conferred the title of king.
Prince Zhao Yu is not a leader of great talent; he is a Dragon Shepherd, in charge of high-ranking positions due to his strength.
If he could be conferred a kingship now, it would mean he already possesses King-level strength!