Because, as professionals, the healthcare team are obligated to do what is in the patient’s best interests according to their training and experience. Legally obligated - as in, open to criminal prosecution, de-registration and litigation if they don’t. Morally obligated, because if you let this one go against your better judgement because ‘he’s already gone, what does it matter. It’ll help his mother’ it’s a slippery slope and you personally are making decisions an individual shouldn’t be making, and emotionally obligated because they have to go home and sleep at night and are (generally speaking) pretty awesome humans.
When people who hold life or death in their hands don’t follow the rules, you end up with Harold Shipman et al. Not in one go, of course. But once you’re over the line you’re on the way, aren’t you?