It's not just that. Compare the GDP per capita of individual US States to other countries. Even the poorest performing US State is still doing better than most of Europe.
Then consider that Luxembourg and Ireland only top the list as a result of being tax havens for the world's rich. The picture looks grim.
Mississippi isn't well populated but most European countries are...so while those countries may be nicer places to live now, Mississippi's future looks brighter.
20 years of totally flat GDP growth capped by a brutal recession was more than enough for Sweden to switch gears and backpedal on an enormous amount of social welfare policy in the early 90s.