Envision for a moment a society where most of the most attractive women want to date the richest guys. And the way to become the richest is to produce things. Conceivably a large group of men would still work despite UBI so they can get with the "hottest" women.
Put this at grand scale and you have why a lot of men bother with anything more than living in a tent by the river. If that production is high enough to actually produce enough necessities it might work, but would require some insanely efficient production.
Envision for a moment a society where most of the most attractive women want to date the richest guys. And the way to become the richest is to produce things. Conceivably a large group of men would still work despite UBI so they can get with the "hottest" women.
Put this at grand scale and you have why a lot of men bother with anything more than living in a tent by the river. If that production is high enough to actually produce enough necessities it might work, but would require some insanely efficient production.