I also wonder why he was kept alive if he needed a battery driven heart. I guess no one has medical directives in the 23rd century?
"Kept alive"? You make it sound like such choices are imposed on the patient from outside. That kind of decision is up to the individual to make. The whole reason Do Not Resuscitate requests exist is because it's the exception to the normal medical rule to do everything possible to keep someone alive. Not to mention that they're intended for cases where a patient is in a permanent vegetative state or in incurable agony, not just for cases where they'd be disabled but otherwise mentally functional and able to go on living. Pike's situation as shown in "The Menagerie" was no worse than Stephen Hawking's, and Hawking managed to continue having a viable and worthwhile life for decades (and even got to appear on Star Trek). Although DSC's retcon that he was in constant agony might change that somewhat, but it would still have been Pike's choice whether or not to have a DNR on file.