Because even with the "super high taxes" you'll probably still earn more than you would in your home country of Honduras or Mozambique or wherever labor will be imported from. People are crossing the border today for a chance to illegally pick produce or work low level construction. Making that easier will only make it more popular. Plus adding a clear path to Citizenship (say after working 7-10 years on a non-UBI visa) will only make it easier to attract people.
As to who gets UBI what happens when you leave a country with UBI, that is an interesting question. My initial reaction would be that you can only get UBI if you are a citizen or permanent resident AND live in the country (say a minimum of 4-6 month out of the year). If you emigrate you lose UBI, but that is a separate discussion.
In most theories I saw, UBI would supplement low wages and become negative only for well off people. So you'd have to pay a nice sum of money for someone to have same take-home pay as UBI jobless. This means UBI countries would need high import tariffs to compete with cheap import from non-UBI.
Now what would be nice is to work illegally in an UBI country.
Path to ubi sounds like a massive Ponzi scheme TBH. Come work for 10 years for an easy retirement. Especially if you can move back to your homecountry and keep earning UBI.
For higher wage, higher quality jobs it might be slightly harder to attract foreign talent, but even with a 20-30% real wage decrease from todays levels the US will still pay more than just about any other country for high end jobs, so it shouldn't be too much of a problem.
Come work for 10 years for an easy retirement. Especially if you can move back to your homecountry and keep earning UBI.
That is why I think it's important to tie UBI to residency rather than just citizenship. If you leave the US you lose UBI.
An absolute sum of money is meaningless in such discussions. In my whereabouts $40-50k would be easily top-10% of not top-5% earnings. Median is a better measure. But how do we calculate median in UBI society? Do we calculate every resident? Only UBI citizens? Only working UBI citizens? Or do we take median pay of today, look what professions it is and then look at what those professions make after UBI?
Personally I'm very skeptical of UBI. IMO it's not possible till all low paying jobs are automated away. Otherwise your solution would create a very unhealthy two-ways society. Sort of like Arab oil states today. Where locals live off oil money and lots of 2nd-tier residents from poor countries are in sort a sort of modern slavery. I don't see how a healthy democratic society could in such a way. There're too many different groups with different incentives.
However setting the levels of UBI is probably not hard part, agreeing how to raise it every year to adjust for inflation and other cost of living increases is where all the problems will come from. I fear the UBI will also require a more dynamic tax code (to control inflation, as postulated by MMM) that will be very tricky to implement politically.
As to the two level society, I think that is inevitable with UBI. Hopefully it won't be as bad as what we're seeing in some oil states, but it will be similar.
Personally I don't think UBI is good idea, but do think it's doable. It will however permanently change the country, possibly for the worse.
Existing salary laws already create a lot of opportunities for arbitraging. E.g. truckers and handymen working in expensive, living out of cars or cheapest houses they can find and then spending their time off (as well as paying taxes) in cheap countries. Country-adjusted UBI could make this even worse. While EU-wide UBI median would create it's own share of issues.
Any idea is doable if you throw enough propaganda and/or gunpower behind it :)
On the other hand, workforce may be coming from another UBI territory with same taxation. What would happen in their former country? Would they still pay UBI taxes to it?