North/West European middle class, for example.
I'm from Finland myself, I've been living in the US for some years, and I have no concrete plans to return. I've known many Finns who have tried the same, but most of them have returned to Finland, or at least to Europe. Most of them are highly educated professionals. It turns out the difference in standard of living is not that large. For most people, living closer to family and friends is more important. If they find a decent opportunity closer to home, they usually take it.
You can see the same effect with Finnish nurses. They could improve their standard of living significantly by moving to Norway. Probably more than software engineers moving to the US. It would be easy, because Norway is close, the culture is pretty similar, and Finnish citizens have a subjective right to live and work there. But few people actually do that.