Why do human beings retire when all it does is make them turn into miserable, unhappy people ?

When I look at retired people including my parents they often seem so miserable.

It is like they don’t know what to do with themselves and as a result they start annoying and trying to control their children and grandchildren and complaining that no one has time for them. However when they were young they had no time for their parents either.

I just feel like if people keep busy till the day they die , they will not become annoying miserable people, unless they get sick of course ( which is different).

As a matter of fact, I have noticed that people that live the longest and are alert in their old age , keep working and busy and active till the day they die.