This is ripe for abuse, they can get paid less than their others in the same jobs, or be exploited by the body shops / mills etc, they move jobs less frequently than someone who would purely have based on career or financial choices, all of which have material impact in the money they can make.[1]
Also it is not unusual for such people to have kids who because they usually born in America are American citizens and may not have citizenship in the country of origin etc, so the risk of stranding the family is also a factor.
Finally English speaking countries generally get more immigrants as language barrier is major factor same reason why U.K. is more desired than other countries in Europe, or Australia/New Zealand are also typically attractive destinations.
For all the negative press about U.S, it is still have one of the largest immigration programs of anywhere in the world and also the jobs that can be had, so it is generally simply easier to get to U.S. and live here than anywhere else.
[1] I wouldn't use inflammatory terms like slavery, however traditionally U.S. has been "built on the backs" of immigrants, First actual slaves and indentured labor(most Europeans up to the revolution came this way ), then poor immigrants. As long as it was better than back home people would keep coming, and as long it was even slightly cheaper than what it would cost locally or jobs citizens won't prefer to do, it will be profitable.
"Why I Became an American" by Enes Kanter Freedom - https://www.theatlantic.com/ideas/archive/2021/12/why-enes-k...
Also, there's nothing special about the US in this case. Germany would probably be an easier go.
It's not that special of a case. For as much as people in the US complain about their government, most of the world is much worse.