You're right, just because robots can automatize production doesn't mean we're left with nothing to do. We still have a job - taking care of ourselves, our families and communities.

A jobless person might be a doctor, an engineer, a farmer or a teacher by training. They don't automatically become stupid by being jobless. They have many needs to fulfill and little money, but lots of time. So they will need to become more self reliant.

The life of a community can be self reliant in many ways - a community could cultivate its own food, build houses, primary medical care, kindergarten and primary school education, install solar panels, drill for water, repair and maintenance for various devices - all of these are needs of local people that can be solved by local work.

If, on top of self reliance, people receive an UBI, it will make it count for so much more, and they won't be just idling around all day long. There is a whole economy that can exist just by providing services to each other.

It has many benefits, including its simplicity. Sure, you could create a framework of incentives and enforcement to make sure only certain people get cash for doing certain things, but those structures will absorb money that might have otherwise gone to the poor. The whole story of international aid, and of UBI if it's done wrong, is a story of propping up inefficient bureaucracies and giving money to aid workers instead of the people who were meant to benefit.