Self sufficient? So youre saying they grow their own food and repair all their own homes?

It's a simple problem of not enough laborers to provide all the menial everyday ressources people want/need, while a growing number of people is retired and still consumes these things. We're technologically advanced enough that it won't cause us to starve, but fewer people making things when the same amount of people consumes things will always lead to lower quality of life if technology doesn't offset it by automating labor.

Capitalism is merely the cruelest system at this, since it will always fuck over the vulnerable first. Under capitalism it's a problem for old people and everyone whose elderly parents are still alive, under a fairer system it would equally affect everyone, but to a lesser degree.