People fleeing Latin America, Asia, Africa, and the Middle East don't focus on the US because we have the best quality of life. We don't; we have a very good quality of life but Scandinavian countries have a better quality of life by any objective measure (besides weather, har har, you suckers). But what we DO have is a remarkable combination of "pretty-darned-good quality of life" and immigrant-friendly policies. Basically all you need to do to become a US citizen is pass a test about the history of the USA and a criminal background check. To become a citizen of small highly-socialized European countries, it's a massive and sometimes decade-long application process with many people denied citizenship, your ability to earn income is questioned, etc...so that they don't bankrupt their highly-socialized systems with a flood of entry-level laborers.
Also, culturally, we're more immigrant-friendly. An immigrant from China may be a Norwegian citizen but he'll never be "ethnically Norwegian." An immigrant from Morocco may be a German citizen but she'll never be "ethnically German." But there's no such thing as "ethnically American." We're a nation of immigrants and, if you're going to be an immigrant, there's some real appeal to getting onboard with that. Once you're a citizen, you're just as American as anyone else. I mean, is there any western European country that has ever had someone like Barack Obama--son of an immigrant, not the majority ethnicity--as their President/Prime Minister/Premier?