I don't know if they've evolved their approach, if my local store is an outlier, or if yours was an outlier, but I live near an Amazon store and go in a few times per week: the experience you describe doesn't match my experience. Over maybe 100 visits: there's usually a few people in there at minimum, the food is pretty good (as far as convenience food store goes) and prices are the same as similar stores. I sometimes have to dance through a crowd of people struggling to get in.

I wouldn't say the concept is a huge success because... it's a convenience store, and location is far more important than anything else, so there's a pretty low ceiling on what a convenience store can achieve beyond being in a good location, but it is certainly convenient.

(As far as business goes, they seem like a cute experiment that has escaped the pointless novelty stage but hasn't reached the industry disruption stage ('cause there isn't one) and so is floating aimlessly in the middle space where they probably can just about justify keeping them around.)