There are a lot of places in the US that are at least as seismically stable and also have more abundant water. I suspect the choice of Arizona has more to do with tax incentives and the fact that fabs already exist there (and thus there is an experienced workforce).
Central Washington is ideal for chip fabs: tons of cheap electricity and excellent infrastructure, massive existing water supply, as/more geologically stable than Arizona, zero hurricanes/tornadoes. Three hours from Seattle is not commuting range, but it's close enough that the chip designers could easily do monthly fab visits. People underestimate how much idea exchange we've lost by separating design from fabrication.
Unfortunately Central Washington is part of a state that is known for erratic, wild, and unpredictable whims when it comes to any company whose name isn't "Boeing". It's not about taxes.
Microsoft, Amazon, Nintendo, etc., have a strong WA presence and what has WA done to them that is 'unpredictable'? WA has no state income tax and is very billionaire and business friendly. You are perhaps thinking of Seattle politics, but Seattle!=WA. WA votes very blue during elections but it's for the pro-wealthy billionaire-friendly blues. WA doesn't elect the AOC squad type blues.
Manufacturing is much more vulnerable, over much longer timescales.
King County runs the state and everybody knows it. I don't like it, but I don't delude myself either.
I recall IBM and other tech companies being called out for occasionally deliberately moving campuses to other states because this creates an excuse to sever certain employees who can't otherwise be lawfully fired.
Micron is a giant in memory device manufacturing, but they don't do logic chips. Memory and logic manufacturing are pretty different, and get more and more different as you get to more and more bleeding-edge processes. Proximity to Micron is nice but not a huge benefit for a foundry.
Lastly, Idaho is gorgeous and the skiing is awesome, but it doesn't check the box for hipsters who want a coastal city. Don't blame me, I don't think this way. But a lot of people do. Anyways Idaho is definitely way beyond driving distance from Seattle.