I know less about Portland, but both Seattle and Vancouver have extremely good local economies and expensive housing and housing shortages.
It's likely that there's a relationship here between people moving to these cities for better economic opportunities, then combinations of misfortune, rising rents and housing scarcity resulting in people becoming at risk of homelessness or being on the street.
Seattle and Portland and Vancouver CA are all overran by the homeless. None of these cities are fun to be in during the winter.
Hell, SF bay area most likely has fewer visibly homeless per capita than the other listed cities.