The store shoppers are usually gathering orders for multiple people. If they weren't there, 3 other "average size Americans" would be in your way.

You know who doesn't get inconvenienced? Me as I sit in my car listening to the radio while someone loads my groceries for an extra 5 fucking dollars. My entire bi-monthly shopping trip takes 15-20 minutes vs. an hour or more inside the store (and also having to deal with the people inside). Money well spent.