Because eventually "work" will be so unnecessary we will need to redistribute money to people who have nothing to do and now that I put that into words I have realized that is already happening at my country, nevermind.
The problem is twofold. First, there’s a lot of people in the world and bringing them out of poverty increases the economy up to 3 orders of magnitude, e.g. from living on $0.25 a day to living on $250 a day, which can suck up a whole lot of productivity gains.
And secondly, as it turns out, there’s always new places to shift demand when less and less of your budget is required just to subsist.
And then when all those “beyond sustenance” dollars all start chasing the same limited supply of goods, say, a house in the Bay Area, or even a lobster dinner…
Land is the only limiter. Even that is cheap if your willing to live in middle of no where.
For me this is the main point of basic income. If you get to the point where people can't consume enough stuff to keep everyone employed, you end up with a situation with the class that own the means of production not having anyone to sell to, because 'the workers' don't have any income.