It looks like Oregon has a 9.9% capital gains tax, so moving to Portland would add to the tax bill of founders relocating before selling their company instead of reducing it.
Oregon also has one of the worst tax regimes in the country. For most earners, a resident of a state like CA without sales tax on groceries, medical care, or medical necessities will end up with a substantially lower tax burden than a similar earner in Oregon. To be more taxed than CA is crazy.
From WA directly: "Washington state does not have a personal or corporate income tax." [1]
Washington can claim it does not have an income tax (for the purposes of subverting the state’s constitution forbidding it), but I do not see how money deducted from your income by government mandate is not a tax.