Okay, Thailand is a very nice country, all told, by Asian standards - it is more accurately a second-world country than a third-world country - but offer unlimited visas to the US and you'd get a lot of takers.
You would get some, from among the poorest. I'm sure if the poorest Americans were offer Dutch or Swedish citizenship they'd grab it. Thais are actually not very prone to desiring emmigration - they really, really hate cold weather, western food, and simply being outside of their rather idyllic culture and in an inferior one.
84 Thailand 2,521
Opebo, here's Thailand for you. About average, actually. Insanely poor by US standards, but the envy of much of the African continent.
72 Thailand 7,901
Thailand does better... but PPP-adjusted, Thais are still earn 1/5th as much as Americans do.
I think that PPP is underestimating the amazing cost of living here - My apartment here is $125/month! That is about 1/4 the cost of the worst apartments in St. Louis. A typical Thai apartment (they don't particularly care for air conditioning) is about $50/month, which is about 1/10th the cost of a St. Louis apartment (the cheapest ones). Of course the cost of living is even cheaper upcountry in the provinces and rural areas.
My meals are not only far better than those available in the US, they cost from fifty cents to two dollars - about 1/10th the cost of similar meals in US restaurants. Again, meals are naturally cheaper upcountry - about 1/2 to 2/3 the cost of meals here in the central, developed region.
Of course there is little or no need for a car here, which is a wonderful savings. Motorbike ownership is preferrable in a country that has excellent weather, and there is the efficient and cheap bus and train service for intercity transport.
In any case, these generalization have little meaning, since the working class is fairly miserable in either country, and the wealthy live in bliss in any land.