How exactly will UBI happen?

UBI is always touted as imminent, but no one actually explains how it will happen? So, how will it happen? Why would someone produce something and then give you money to buy the thing? If someone owns a factory that manufactures stuff, if he gives you 500 dollars to buy stuff worth 500 dollars, he didn't make any money; what happened is that he gave you 500 dollars, and then you exchanged 500 dollars for stuff worth 500 dollars. So, the factory owner exchanged stuff worth 500 dollars after giving you 500 dollars (you game them back to him). In this scenario, it's a zero-sum game. As for "taxing wealth", math still doesn't work. You need many, many trillions to support UBI than there are in the whole US economy. And if taxes are the answer, why would the elite just stay there and watch instead of lobbying the privately-funded parties and politicians not to tax the wealth? We have millions of unemployed and poor people, including homeless, right now, yet we don't see UBI for them. If we can't have UBI when there are millions of people who don't have money, why do we assume we will have UBI when there are BILLIONS of such people? If we can't help millions, we can't help billions for sure. I don't see it happening. The notion I will be getting free money for existing in a coach doesn't make sense. I don't see it happening. Am I missing something?