They originated in the rural Pacific Northwest, because coffee culture isn't just in the city there, but they've spread across the northern half of the Mountain West. This is a very regional bit of Americana, most Americans aren't familiar with it unless they've driven through the backwaters of that part of the country. Sometimes they are truly out in the middle of nowhere on county roads in the wilderness and such, no other buildings for miles, the novelty of which delights people the first time they see it. Small rural towns usually have multiple espresso shacks.

The coffee is legitimately very good in my experience. It is common in that part of the US to drink coffee with neither milk nor sugar.

Here is nice blog about them with a ton of pictures:

https://roadslesstraveled.us/coffee-kiosks-of-the-west/

Google does: https://www.google.com/search?q=espresso+shacks&tbm=isch

Looks like there's a lot of crossover with the "bikini barista" concept, which I could picture being off-putting to some. I guess that's another plus for a national chain— your morning coffee isn't going to turn out to be something embarrassing to have to explain to the kids in the back seat.

I think it's really the northwest. Oregon has em, but driving from the bay area to LA I never saw one in rural parts of central california. They might exist though.