what your describing basically sounds like "trickle down economics" for UBI. you really think if we dump public funds into the private sector, they'll just redistribute it to the public? look at the world we live in now, and it should be apparent how unlikely that is.

implementing any sort of UBI would require a shift away from an exclusively capitalist framework, so trying to frame it in terms of current globalized capitalism is just going to lead to a lot of dead ends. consider that if a future really becomes "post work" as some people theorize (i do not think this will happen tbqh, but i am open to it conceptually), that will come with massive social upheaval. revolutionary social periods tend to spring up when people have a lot of time on their hands in addition to knowledge and a cause to fight for. hopefully, over the next 60 years we will see a transition from exclusionist socio-economic structures to holistic models that incorporate facets of all existing theories with some new ones. this has notably been the trend of every academic, scientific, and artistic field as we have entered the transition to the age of aquarius over the past two decades, so it is not unlikely. if we live in a truly post work society, people will have enough time on their hands to force such new social structures, and UBI on a public level or other equivalents would likely be on that list (assuming a better alternative is not developed by then)