Trust Fund Paradoxon:
As "The millionaire next door" has shown, people who worked hard for their money are way more frugal then those who have inherited it. That also applies to the children of those hard workers.
However, regardless of those circumstances most of the people today, especially in the USA, are consumer suckas. They may work hard to get the 6-figure, but they also spend hard.

The most important point in deciding if a child will be frugal is - surprise! - the leading and example of their parents.

But those frugal parents have a problem - our earth destroying consumption society. Funnily that is the same that would keep the producing going on if you introduce the UBI.
That would also prevent a sudden collapse of production. (60% of people say they would work the same or only slightly less hours if they had an UBI)
It would also make sure, I think, that there is a (mostly) sufficient equlilibrium. (A few people always need more, like old folks with Alzheimer).

Talking about Alzheimer: About half of the work done is NOT payed. That mostly applies to much needed social reproduction work (reproduction here does not mean children but e.g. caring for the Alzheimer people). Havin an UBI would increase the affordability (time and money, really interchangable here, if you have to work, you have no time) for such work, especially in the care sector. That on the other hand would save a lot of money (one care place costs about 3-4 times of an UBI and has only bad service because of not enough people, and then even those few are badly paid, especially compared to the work they do)

And then there is of course automatisation. It is the easiest to see in the farming sector: 200 years back 3/4 were working on producing food (german numbers), today its about 3/4 of an %!
Other productions have also increased tenfold or more per head.
The computerisation and the robotisation will do this for other parts of workforce too. It should be possible, even with current technology, to make an automated waste collection truck for example.

100 Years back Keynes predicted that the people would only work 15-20 hours per week.
You laugh?
Well, he didnt predict computers and TVs and other expensive items that add a few hours. Or expensive cars that every family member has. He also didnt predict that house sizes would triple in the US in those 100 years. That are his flaws.

But it is perfectly possible to live on the sizes of 100 years back, with modern improvements (like heating), with just 15 hours of work a week.
In the US, once you paid for your house, you can easily live on 20K a year for... no, not one person, but 3 people. And you can easily get a perfect house for ten times this.