I think it has to do with the turn-on effect. Being locked up during a cuckold session is one thing, but the concept of being locked up permanently is the same feelings and arousal, but like 100x the intensity. I don't want to be locked up permanently, but the idea that I might be locked up long-term both frightens and excites me, and the longer the suggested lockup, the stronger both the fear and arousal and other mixed feelings are, which is the chastity cuckold experience. Permanent lockup fantasies turn me on even though I know I couldn't ever consider more than a week or so at most.
