They were under orders not to leave early under those circumstances. Simple as that.
Not only that, it's straight out of the Code of Conduct.
" If I am captured I will continue to resist by all means available. I will make every effort to escape and aid others to escape. I will accept neither parole nor special favors from the enemy."
LOL, guess a few others noted that before me. But what the heck, it was worth saying again.