Humans are specifically incentivized to be efficient at scale. They'll tend to shop at loctions on the way home from work, or otherwise cut down on travel times because traffic sucks.
I honestly can imagine that Costco is overall more efficient than Amazon, especially for people who do shop at Costco. If there's no Costco closeby, its more likely that the individual humans will shop elsewhere or somewhere more convenient.
this isn't even close to true and falls apart in a number of ways, the most popular vehicle in america right now (F-series truck) is woefully inefficient for just about everything
there are people who regularly go out of their way to drive to their favorite store for like 1-2 special items, people bring their dogs along on trips for companionship and leave them sitting in an air conditioned idling car while they shop
individuals are irrationally inefficient in dozens of ways that large businesses root out, for better or worse
I honestly don't know where the nearest Costco is but it's nowhere convenient.