The US is EXTREMELY happy to collect taxes from people around the world and to call them resident aliens for tax purposes if they stay in the country for more than half a year or a given combination of days in the preceding 4-5 years.
I am not a citizen, but pay taxes(not US). In most cases it's not the citizenship that matters for taxes, but person's fiscal residency and normally it's where you live more than 6 months in a year.
Of course, being a US citizen it's a little bit different, you have to declare and sometimes pay the taxes in different countries.
Why would a non-citizen not pay taxes ? If you're settled somewhere legally and earn money, you're going to pay taxes. It's pretty much universal (aside from certain tax heavens and countries too weak to even collect taxes)
The US is EXTREMELY happy to collect taxes from people around the world and to call them resident aliens for tax purposes if they stay in the country for more than half a year or a given combination of days in the preceding 4-5 years.