>In that case, we wouldn't have people living in coma for years.

It's expensive to maintain and many of these are taken off lifesupport before a few years, because what's the point when even their brain is atrophying?

>Also countless elders are doing fine staying in bed all day.

Doing fine is a massive overstatement, their muscles atrophy, they need help with everything, their risk of infection increases. And if you're awake and in bed you're still moving around and compensating position for where it starts to hurt.

I've been working in elderly care and seen patients with a long range of neurological issues and those that are just bedridden but conscious and mobile are enormously much less work than the ones with no remaining motor function and minimal responsiveness. You need more than 1 person on full time employment for each of these patients, even more when the person needs physical therapy to maintain range of motion. Their immobility leads to lots of additional problems which inevitably shorten their lifetime.