I don't know the overall ratio, but my experience working with many immigrant workers is that they had no real intention of staying and instead are just arbitraging cost of living between [rich country] and [poor country] for their family back home. Emphasis on home.

Sounds like you have a really limited interaction with immigrants. I’m lifelong immigrant (4 different countries) in every single one of those countries majority of immigrants want to stay. Permanent residency is a constant conversation topic. There are definitely immigrants thinking like your explanation, but definitely a minority. .

There are all sorts of reasons people emigrate. It varies based on the jobs they’re doing, where they’re from, and where they’re going. And whatever their intentions, things change. And, why must there be a universal answer for everyone?