Normally, I'd agree with you, but the Portland-Seattle HSR corridor is around the low end of viable HSR corridors. You're connecting the 17th, 27th, and 28th largest cities in US+Canada, with no realistic prospects to connect anything else approaching a major city--the next largest city is Boise, but that's 350mi away as the crow flies (and mountains means it's quite further in practice), and smaller than even places like Fresno/Bakersfield, which people complain about CAHSR considering to visit. Oh, and one of those three cities is on the other side of an international border, which tends to dampen ridership a fair amount.

By contrast, all the other standard HSR candidates anchor regions that involve at least one, and for all but the Midwest two, cities in the top 10, with many more in the top 50.