It isn't about productivity by itself. It is about aligning production with consumption. It is wildly naive of Westerners to believe there is so much excess production in the world that we can just pay people to not work. The US got their "UBI" in 2020, and it was Americans sitting around while foreigners labored in factories, docks, and ships to produce and deliver the consumed products.

Yes, there is a tremendous amount of waste in the global economy, but if we want to improve quality of life then we should focus on the mechanisms which cause that waste in the first place (e.g. targeting GDP growth.) If we solved those excesses (a very tall order), then why would it be fair for one group to be over-consume at the cost of another groups over-production?