The article actually mentioned this.
"For the purposes of this field guide, we have laid down parameters. A hamburger is a marvelous sandwich, but it is one deserving of its own guide. The same holds for hot dogs, and for tacos and burritos, which in 2006, in the case known as Panera v. Qdoba, a Massachusetts judge declared were not sandwiches at all. Open-faced sandwiches are not sandwiches. Gyros and shawarmas are not sandwiches. The bread that encases them is neither split nor hinged, but wrapped."
Fair enough, especially since they called out this distinction so clearly. But yeah, no doubt the void you've noticed is almost certainly related to the taqueria culture on the west coast [1].
It's not that sandwich shops don't exist on the west coast -clearly they do, and some of them are pretty good. However, we just don't have the sandwich culture out here. How can you tell? If you're in the mood to stir something up, just ask a couple of people from that region where to get a really good sandwich, and see if you start an argument. See if that argument turns surprisingly personal.
Now, try the same thing with burritos, and you'll get whole different reaction. You may also hear that burritos are vastly better in SF than in SoCal, or you may hear that the question itself is all wrong, because burritos are properly listed as a minor niche item on the bottom right menu of genuinely good taquerias, which you only find in SoCal.
I've been west coast my whole life, but I get the feeling that's the kind of status sandwiches have on the east coast.
[1] I originally considered changing this to "California". But a guy who lived in Seattle for 7 years told me that a taqueria up there (there's my great cite) sold "Mission Style" burritos in reference to the mission district of SF. So, on the basis of that remarkable bit of information, we'll stick with "west coast" here.