From what I found, Seolrang is obsessed with the idea of marriage because for her is the only way they can become family. Like leon mane=family, boss=not family, how can boss become family if he isn't part of the leon mane tribe? Marriage. Kinda dumb and innocent.
And Yutia reveres him like a god, so she sees Seolrang beneath his greatness or smth.
And above everything else, he thinks of them as his children.

I was enjoying this so much, imma drop this shit if it's going to become a Harem and I really hope the kids stay as his adopted children and not wife's