For starters, easy access to one of the largest (and in many cases highest paying) job markets in the world. Secondarily, a high quality fallback in the event of significant geopolitical or environmental changes in ones new host country.
In the hypothetical scenario where an emigrant from the US is 100% determined to never return, and who also is confident in the long term stability of their new host nation - then the inconveniences of yearly tax paperwork might outweigh the benefits. However, I think that's more of a corner case than not as evidenced by the fact that the vast majority of emigrants choose to retain their US passport.
Being able to return to the USA, and visa-free access to more/different countries compared to the new citizenship.
Renouncing American citizenship is extremely rare, as these figures show. The taxation is a paperwork hassle, but you need a very high income to actually owe anything -- for most, the higher tax rate in the new country offsets the American tax due.
This is a big misunderstanding of US taxation. Every US citizen must file their taxes on income earned anywhere in the world, even if not earned in the US.
However, for most people, it is very unlikely to actually pay any additional tax to the US government.
If you have any kind of saving or investment outside the us, say, a pension fund or a mutual fund, then you do owe quite a bit even if you live in the US (more if you don't). Almost all of these investments/funds are a PFIC by US rules, which means a world of pain - to the point that over 20 years you are likely to have to pay more in taxes than however much money you have there.
After you make $100k, there is also the foreign tax credit. In most countries, you don't need to bother with the foreign earned income exclusion unless you are not paying tax at all.
It gets WAY more complex if you don't have a standard salary job. Even if you don't make over 100K a year. E.g. small business owner expat is in for a world of pain, stress, and audit.
You cannot/shouldn't renounce your US citizenship for tax reasons. [0] Every piece of advice you read from anyone online will say the same thing: if you must give a reason for expatriation (and you don't have to), say anything but taxes.
You don't officially have to give a reason to renounce, but consular officials might ask you verbally for your reasons. You are not required to give one though. You have the option to include a written statement, but I'm not sure why you'd ever want to take it (unless you really want to give them additional reasons to deny you entry).
If they determined you did for taxes, it's a no-no:
Former U.S. citizens would be required to obtain a visa to travel to the United States or show that they are eligible for admission pursuant to the terms of the Visa Waiver Program. If unable to qualify for a visa, the person could be permanently barred from entering the United States.
If the Department of Homeland Security determines that the renunciation is motivated by tax avoidance purposes, the individual will be found inadmissible to the United States under Section 212(a)(10)(E) of the Immigration and Nationality Act (8 U.S.C. 1182(a)(10)(E)), as amended.
https://travel.state.gov/content/travel/en/legal-considerati...
I don't think you understand how taxes work. US tax rates are marginal, so for your effective tax rate to be 30% you'd probably be earning several million dollars in payroll. Very unlikely. Not to mention the fact that if you're an expat, income tax paid in your country of residence counts toward your US tax obligation.
If you live somewhere with higher taxes, you owe the US nothing. If you live somewhere with lower taxes, you owe only the difference.
Speaking as a wealthy person who has considered expatriating, the US is REALLY nice relative to almost anywhere in the world if you have a lot of money. There are also activities like piloting your own planes, using wide-open spaces, etc, that are much more regulated and hard to enjoy in other places.
US is also really fun for girls/partying if you have money.
30%+ of your income down the drain sucks a lot, but past a certain point in net worth it becomes somewhat attractive. Same reason people live in California even with the insane tax burden--it's really really freaking nice.
In the hypothetical scenario where an emigrant from the US is 100% determined to never return, and who also is confident in the long term stability of their new host nation - then the inconveniences of yearly tax paperwork might outweigh the benefits. However, I think that's more of a corner case than not as evidenced by the fact that the vast majority of emigrants choose to retain their US passport.