And? Sorry I still don't see your issue. Are American car parks so ill designed that they're aren't wide enough to allow two cars to pass?
There really is no issue here.
If you feel so strongly about this, why even physically go shopping? Most supermarkets here do a home delivery service after ordering online and you can buy most other things online aswell.
Many parking lots in the U.S. aren't designed very well at all, and the smaller the market or shop, the more poorly designed the parking spaces.
I do understand that it gets annoying when you're still putting away your groceries or bags in your trunk, and there's a guy sitting 3 feet away in his car, with his signal on, just waiting to get into your space, and he's so close you either can't maneuver to get out, or that car has sat there so long (through no fault of your own), that it's letting the whole section become congested, and now no one
can get out until that car moves.
The polite thing to do, if you're looking for a space in which to park, is usually to wait a few seconds, and if it doesn't look like the car is leaving anytime soon, to go around and come back. That gives the car a chance to leave, and keeps traffic flowing.