It just isn't, I can quickly and easily park my bike in basically any spot. If I know I'm not buying a lot I'll just bring a backpack and put my groceries in there as I checkout and if not I probably brought the scooter which has the same trunk as a small car.
I don't have to fuss about in traffic, look for a spot, or try to turn my car around in my tiny neighborhood. (Not the fiat...I do own one of those oversized American cars that's literally 18.5 ft long because it was cheap)
But hey maybe I'm just dead wrong, give a bicycle a try. (If possible I recognize not many north American places are bicycle friendly) try getting some groceries on a bicycle. You might actually enjoy the benefits, yes it'll be tough the first time and likely even the fifth...but you might come to enjoy it.