Because the organization tries to enforce compliance via undue influence, i.e. coercion, manipulation, implanting of phobias, publishing of old and misleading data, shunning, etc, etc. -Lee
I think that you are misrepresenting WT on this thread. WT does not coerces any JW, not to commit adultery, apostasy, etc. nor coerces JW not to accept BT.
More than one loved one besides many friends are physicians. They receive special training on how to handle JW patients that need BT. Not every doctor understands JW theology on blood but it doesn't matter, they are very prepared to give blood to any person that wants it. Even after all papers are signed, a doctor may go up to a patient right before anesthesia and ask again his wishes and do everything in his power to convince a JW to accept blood - after all it is a doctor's job to help the patient.
A JW doesn't have to sign the card, doesn't have to carry it and can do whatever he wishes. It is between him and God. As I have pointed out numerous times, accepting BT is a sin according to wt teaching. According to wt doctrine, it is not up to personal conscience to commit idolatry, sexual immorality or accept a BT. But a person can commit these sins and repent. People can live a lie also if they want to or choose whatever they like to do. God is the final judge.
