Actually they do offer something of a theory: It's Barack Obama's fault.
Really. We all remember "strategic patience," right? That was Obama's slick-sounding name for doing nothing about hostile tyrants and thugs while trying to make it sound like a strategy. Well, you understand, old strategically patient Barack never bothered to ask for Wambier's release. Otherwise, I'm sure Bowl Cut Jr. would have handed him right over, no questions asked.
That must be it. Torture? Deprivation? Beatings? The glorious shining kingdom of the DPRK would never do anything like that: