Interestingly, all except two are in the far west. I've never been to an Eastern national park, but I would have thought they'd be strong in the day-hike department.

Well there's lot of hiking in eastern parks, but the terrain is mostly hundreds of millions of years older than the west coast ranges, with the exception of Acadia which was scraped into interesting shapes by glaciation. Shenandoah is beautiful, the Smokies are beautiful, but nothing even close to the younger geology of the West.