Because I have read several books and listened to several hours worth of academic lectures by economic professors on the matter. I don't care if it's a state stipend, a negative tax credit, a special fund of some kind.

The closest to functional UBI happened in Libya, when people were given shares in nationalised oil companies, and the people who advocate for UBI also advocated for bombing that country and bringing back the slave trade. Partially in an effort to use their oil in order to fund parasitic welfare states that permit rich people to still be rich.

Ending first world poverty by creating third world poverty is not a solution, and moreover, it doesn't even work. People on welfare are just as miserable and alienated from society, they just get to be miserable and alienated indoors. There is no alternative to nationalisation. For as long as capitalists drain the economy, conquered peoples across the world will have to pick up the bill.