We'd probably need a degree in economics to model this, but intuitively I'd think it's both a matter of relative difference in wealth being much smaller between Cali & Louisiana than between Germany&Romania, as well as the absolute living conditions being much better in Louisiana than Romania.
There's poor, and there's poor. Nowhere in the US or Western Europe is even remotely poor like post-communist Romania was poor. That changes the game a lot when deciding where to live and work.