It was a long time dream/plan of mine to try get sponsored and on to the green card system (because I think the US is a beautiful country - and I would love to live there for multiple years) until I discovered these taxation laws.
Over the threshold, you only pay taxes if you live in a country where taxes are less than the US, which is, to be honest, not that many countries.
It's (sort of) that simple for earned income. In another country you may throughout your life receive money from a wide range of sources (health benefits, health recovery, child benefits, pensions, scholarships, the list goes on...) - the US tax status on these is incredibly complex at best. The punishments for making a mistake can be severe.
Also the US has now imposed laws that require financial institutions to report to the IRS if you are a US citizen. I'm not in the financial industry so can't verify first hand, but all reports are that the paperwork and reporting burden is significant. So much so that many banks now have a "no US citizens" policy.