Wanting to be financially independent doesn't necessarily mean you want to completely stop working. It just means you want to choose how you spend your time.
The point is if you sum up what people would want to do with their time, there's no reason to expect that in any way corresponds with what the allocation of resources should be to keep the engines of the economy moving / achieve maximal societal benefit / whatever. It's a classic tragedy of the commons situation.
Yes, check out /r/financialindependence
There's thousands of people living frugally to retire early with ~1-2 million which is basically UBI over a lifetime