I genuinely do not understand what they are trying to achieve with this method of management.
Right Engine
They are trying to fulfill the terms of their employment as dictated by
British Airways. If they stick rigidly to the agreement it is because that is what they are employed to do. You are assuming that BA gave them a choice which is not the case. If the company wants more flexibility then they will change the system but in the meantime the DOMs, like many of us mere employees, are not employed to make up their own minds so your beef is with the company and not the DOMs.
I suspect that historically the reason BA has told them to stick to the rules is so they don't have the CC unions kicking off so potentially this all could be open for change.