A lot of people don't realize that after the hospital gives you morphine for the pain, you're unable to communicate so you can't make your wishes known, and you can go downhill quickly. The family members, when consulted, are anxious to spare the person pain and thus acquiesce to no resuscitation.
I can attest to this from personal experience. After having an operation and being given morphine for the pain, I got agitated when no one would answer me when I spoke to them. Turns out, I wasn't "talking" out loud. Pretty spooky.