1. Brat breeders' boarding school allowance, or whatever it's called now - they couldn't afford to leave.
2. Being in an aircrew trade which has little or no commercial attraction - no outside jobs.
3. Being someone who has shafted JOs in the past in his quest for stars, now thinks about PVRing. Suddenly discovering that the ex-RAF mates airline jungle drums have black-spotted him for ever, so has to stay in as there is a "If you ever get an application from this d*ckhead, throw it away" memo in most airline recruiters' offices about him.....