> In a lot (most?) of the US most places are far enough away [...]

I've never seen a grocery store with a parking garage (opposed to a parking lot) that wasn't in a city. If the grocery store has a parking garage instead of a parking lot, then it is almost certainly in an urban area and public transit and is within walking distance of many residences and businesses.

This is in fact the case for the particular Trader Joe's in question. Look up "Trader Joes’s at Hollywood and Vine". That neighborhood is easily walkable, has at least some public transit, and their parking garage is within easy walking distance of numerous other businesses.