1) it’s a relatively new city built with money generated by proximity to Microsoft, and because it is new and expensive, and populated by an almost entirely college educated population, it has not (yet) accumulated an underclass.
2) Seattle/bellevue/redmond started as a heavily Scandinavian lumber and coal region, but never experienced the migration of black communities off the farms during the automation of farming and the war era. Ergo it is a very “white” area, with Asian and Hindu minorities.
3) Nor is Seattle one of the traditional Gateway cities for processing the first generation or two of immigrants.
4) In addition, the northwest is ‘hard to get to’. The weather is grey and wet. It is painfully dark much of the year. And so it attracts a certain class of person.
We have a joke that Bellevue is a “Green Zone”: a beautiful place to live amidst the rapidly declining majority of the country, simply because it is a rare artificial economy, and it’s too expensive to survive there, and there is no demand for unskilled labor (Those people live north in bellingham or south in Renton.)
Impolitic as it is, if you want a nice region the basic problem is to keep out the lower classes. Because the lower classes demonstrate undesirable behaviors that decrease the quality of territory, institutions, capital, norms, schools, shops, neighborhoods, homes, private property, and family life.
Europe is a vast open air museum because for thousands of years they practiced land allocation by merit, manorialism, late marriage and child birth, prohibition on cousin marriage, and hung about 1% of the entire population every single year. By the industrial revolution most of Europe was descended from members of what we would call the middle social class.
Just how it is. If you want comforting lies, ask college professors and the media – they get paid to tell you what you want to hear.