Most of them are part of old cities that are past their prime in economic vitality, so those areas don't have the same liveliness as what you might get in downtown Boston. (I used to work for a company based there, and would spend hours walking around at night.)
I'd recommend Pittsburgh for walkability, too. It's one of the most delightful cities I've wandered around recently.
Unfortunately, even Boston, Pittsburgh, NYC, and the lesser-known but walkable/dense areas are pretty unappealing when compared to some cities in south/central america and Europe, that were built before cars took over everything.
I suspect once a few large cities go bankrupt and cannot enforce their zoning regulations, new construction will move in the direction of rational density again.
This said, the only reason why Hoboken and many other walkable cities can get public-support for being so walkable (and encouraging city planning as such) is the ample public-transit options.
This leads to no need for having a car which leads to most people not having one which leads to most people preferring walkable versus drivable. It's kind of a chicken-and-egg problem.
Portions of Seattle are very walkable (From the International District going north, quite a few miles), and individual parts of Chicago are walkable. Heck there are 2 or 3 mile stretches of San Diego are walkable (there might be more than that, I only spent a week there!)
Seattle, on the other hand, is a city where I’ve never really needed a car no matter where I lived or worked. I think that part of the lifestyle is brilliant. I have a car, but the battery goes dead between usages as often as not.
Seattle has plenty of walkable parts, but I grew up in a working class suburban neighborhood within the city where driving to the store was most certainly necessary.
Some individual portions of Chicago are very walkable. Likewise with some small bits of San Diego, though you are right, not as good as European cities.
The entire city is only 7 miles wide, so about half the city is within a 30 minute walking radius.