Don't laugh, but it's a kind of patriotism.
I love the country. It's beautiful. I like its philosophy. American values resonate close to my values. In the years I lived there I grew to think of it as my home much more than the country I was born in. I could see calling myself American.
When I went there I was received well. I was helped. I made friends. Now I think I can help in return. I would like to contribute, especially in a downturn. I would buy a house, I would create jobs.
Now, I travel a lot (including in US) so I live all over the world. And financially I'd have little to gain in States (no extra income, higher living costs, higher taxation, higher business costs). So it'd be mostly an idealistic gesture, a way for me to participate in building something larger than myself and what I've already built. Something I truly believe in.
But I am not getting myself again in the Kafka's nightmare that US immigration is. Waiting years for some bureaucrat to decide if your life will go on or will be completely changed "just because". No thanks. I'd only consider another country if I'd have a clear, legal and quick path to residency. Otherwise... I'll only be a tourist.