How long will it last

My grandfather was supposed to be transferred to a hospice today, where he'll rest and be under the care of doctors and nurses (for the rest of his life). But the doctors said that it is useless now 'cause my grandfather has no reactions. I thought he has, he occassionally raises his eyebrows and hands! And they said that his body is already not functioning but the heart still beats. Now we're like waiting for it to stop, we can do nothing else, nothing more. I don't want him to die. A few months ago, my grandfather still looked healthy. Just a few months, and such drastic changes occurred.
Why is it that we always start cherishing people around us only when we are about to lose them?