Because it favors social cohesion and social trust, which are strongly correlated with economic success. Americans are reflexively thinking of race, but that's entirely incidental and basically irrelevant.

It's not even true, 40% of the population has an immigrant background. And as for low crime, yes, blue collar crime. Please don't ask about white collar crime, we don't talk about that here...

It's a dog whistle for "if a country's racial identity remained pure everything would've been fine".