I would think that 'roots' would be a big drag on mobility in pretty much any city. So I don't know if that's a factor in Portland's unique 'problem'.

And someone who never thought to question their salary level is by definition someone who couldn't be conscious of any trade-offs that might be in play.

Is everyone aware? Almost certainly not. But if you ever had cause to look at salary data, I don't think you could miss it.