In any case, the fact that a significant number of people opt for organ or body donation suggests they are willing to allow their deaths to be useful to others in some way.
For some that motivation might be strong enough to be willing to undergo some discomfort (if, indeed there needs to be any discomfort in the first place, which isn't clear). For others, it might not be.
The fact that you personally would be happy to be an organ donor but would draw the line at having an ECG while dying is a perfectly valid position to take. Many people would no doubt take the same position. It's unlikely though that 60-70 million people per year would all react that way. Neither of us has to be right or wrong here (about the difference between the two scenarios), because it's other people's motivations we're talking about.
I'm curious about my death, too! I've sat with people who are very close to that edge, and I realize it's the last experience I'll ever have, the last lesson I'll ever learn, and find it poignant that I won't be able to tell anyone else about it. Being part of an experiment like this would be... satisfying, somehow. It feels like it would give meaning to my death.
I respect that you have a different point of view, but I hope that helps you understand what would motivate someone to do something like this.
Because they care about leaving behind an impact after they die. I don't think it would be for everyone, but there surely be some people who would want to do this.
not all of it, presumably, if you want to express your distaste on the magical glass slab and you want pain killers on your way out.