Why must I marry a saintess who was summoned from another world?

A saintess was summoned from another world. There is a custom that the saintess must marry into the royal family, and the only one in this country who is not yet "married" is the crown prince alone. However, he already had a fiancée. "Why must I marry a saintess who was supposedly summoned from another world?" I was thinking, why do saintesses and crown princes so often fall in love in web novels? So I wrote this short play about a saintess who was summoned from another world due to the rampage of some people, in a situation where only level-headed people are gathered. Hmm, I feel bad for the saintess in this story...