I mean, I sort of imagine it to be less the "rule on the books" part, and more the "do we actually have the physical capacity to enforce those rules" end of it. They cant really imprison him (I mean while he's feeling guilty he might stay willingly, but they cant keep him in if he eventually changes his mind, so itd more be him imprisoning himself). Trying to despite the futility of it would seem somewhat dangerous, because again, if he should ever change his mind, you clearly dont want to seem hostile to something with that kind of power, especially when you dont have it. Saying "Our law is not sufficient for you" could just be interpreted as the most diplomatic way given his mental state to justify leaving and not returning.