UBI makes little sense whenever someone making 500K a year still gets it unconditionally. The marginal utility of that is nil, but its tax implications are massive (how do you even fund something like that in today's economy).
Even if you make twice as much as the negative income tax floor, you're still facing really high marginal rates. Enough people would drop out of the market economy to make the negative income equivalent to a basic income in financial cost, but more inefficient both because low income jobs would be obliterated and because it'd be (a bit) more complicated to administer and more prone to fraud.
Compare that to a basic income. There, as a first order effect there's no reason for the person to quit the 12k job, because they're now making 24k.
It might seem silly to give someone making 500k 12k a year, but economically and fiscally it doesn't matter: they're taxed at a rate that covers their own basic income and plenty more.
Alternatively, you could say that--even with non-NIT UBI--since we have a progressive tax structure, the net change in taxes for people above some income level will be exactly the same net change in taxes as NIT is proposing. The money has to come from somewhere after all.
Everyone gets the UBI, but the more money you make, the more you're paying in additional taxes to support the UBI. At some threshold you're paying as much in additional taxes as your making in UBI payments. Past another threshold and you're paying more in additional taxes than you're taking in.
I don't find this especially convincing, since from a purely rational point of view decreasing UBI increases net income for the rich. But maybe there are complex psychological/political factors at play.
Then there's no reason to work at the lower end of the wage scale, because you'd be working for free.