I don't think only UBI will remain. People will be getting money through a lot of different schemes, some merit or effort based. So there will be ways to climb. Just not through "hard work" because the "work" part is going to be mostly missing. To see how climbing the ladder might look in the future look at spots in our society that perform no useful economic activity. Military, prisons, government offices, the rich, homeless. How you get ahead there is going be the way you go ahead everywhere in a society where human work is obsolete.
> why would businesses need everybody to participate when a specific portion of people are enough?
For business nothing is ever enough. It creates products and customers for them out of thin air. The only required thing is money in the consumer pocket. Business itself is going to pressure governments to give more people more money, by whatever means necessary, so it can scoop it up off of them.
What even some millionaires now realize is that it's very hard to take the money away from other millionaires. They don't spend that much. But if you tax them and give the money to consumers, suddenly, as a rich person, you have clear path to taking this money for yourself, just by having a successful customer facing business.
That (among other things) is why some rich advocate for higher taxation of the rich.
If everyone around you is poor it's very hard to get any richer yourself, regardless of how much you already have. And rich people like getting richer most of all.
