My reasons? Family and climate.
I grew up in Western WA, and just moved home after 26 years of exile, mostly in PA. The sweltering, humid summers (mid May to mid September) were the worst. The hard winters (mid October to mid April) I could tolerate. Most of my large family are in western WA as well.
Why Lewis County sucks less than other WA counties:
Lewis County is the most rebellious county on the soggy side of the mountains. For example, Olympia decreed that all new construction should have to pay additional "impact fees" that were supposedly for infrastructure. This adds a hidden cost of tens of thousands of dollars to any new home. Lewis County said, "Nope. Not gonna do it."
There are also lots of good, decent, hard-working, blue-collar, salt of the earth types here. Most are still asleep, of course. Cost of living is very low compared to the Puget Sound area. Snobby people are practically non-existent.
Lots of wildlife. Good hunting and fishing. Land is MUCH more affordable than further north.
Oh yeah. Legal doobage is nice.