Many here believe that if people weren't forced to work for income, they would be doing things that are more valuable but also more difficult to monetize (at least initially but perhaps generally), like open source development. There is an underlying belief that vast creative talents are untapped or wasted because of the need to work for money. It's the intellectual's dream lifestyle. One that used to be possible for writers and academics.
Other reasons are largely an afterthought. That's why basic job for example is not a convincing counterargument despite the numbers. This is not really about helping the poor, that would be an auxiliary benefit at best.
[1] https://www.chrisstucchio.com/blog/2013/basic_income_vs_basi...
