Prisoner's dilemma has a Nash equilibrium where defection is the best move regardless of anything else that happens. If you change the game to be a repetitive 'prisoner's dilemma' with the same actors the best strategy would be tit for tat.
That's why underlings have strong incentives to defect, and defect quickly. (Defection is also rarely an option for the person at the top of the pyramid.)
Caroline's option to save Caroline regardless of what Sam does by testifying looks a lot better.
SBF’s situation is different in that the game ends as soon as someone defects.