No, no rationale. The oath breaking/keeping logic in this first paladin release is wonky in the extreme. I’d just recommend adding your thoughts to one of the existing paladin oath threads and hopefully Larian will review these and take on board for the full game.

E.g. https://forums.larian.com/ubbthreads.php?ubb=showflat&Number=838755

Or https://forums.larian.com/ubbthreads.php?ubb=showflat&Number=837719

"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"