Amazon generally doesn't do single item delivery for perishable groceries though, Fresh has a $100 minimum to avoid fees, for example.

Non-perishables are fine on a single-unit purchase because again, they're not just going to your house, they're going to dozens in your area every single day.

I know where you're coming from, but there's a reason this whole model exists, and it's not because it costs more.

Well sure. But Costcos model is clear to anyone who visits it. You only have to look at all the other shopping carts surrounding you to get an idea of how things work.

Costco shoppers buy a lot at a time. Because Costco forces you to buy 4 tubes of Toothpaste, 24 eggs (or 60 eggs), minimum 1 gallon of milk (no half gallons or pints), and like 20 lbs of rice / 10kg for the Europeans who havent been here and like 3000 meters of plastic wrap.

For Costco, the efficiency is the shear size of the shopping carts and shear mass of the goods sold at a time.

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You literally can't buy only one bar of soap or one toothbrush like you can from Amazon.com or other stores. There's efficiency here because of simple mass.

In contrast, I can look out and see the Amazon packages in my neighbors doors. It's all single items across the neighborhood.