Where are you getting this data? I've known many monks (and nuns too for that matter) and you are encouraged to discuss when you are unhappy. No abbot wants a miserable monk, so they work with you to be sure you are happy and adjusting well to the life. If not, then you mutually come to a decision about what to do next, even if that means leaving the monastery. Implying that they are some sort of prisoner is inaccurate.