Morrin has waited a long time to claim his throne, and even longer to have a real family. It may not be a conventional family, consisting of his closest friends, his brother Istari, and Istari's spouse and children, but it's one he loves and is proud of. No odious brothers, no abusive father, no cowardly mother.
The very last thing he wants is to upset the balance by taking a wife, but his friends are right in that seeing him married will go a long way toward repairing the damage caused by his war-mongering, tyrant father. He just didn't expect them to suggest the blandest princess in the castle.