> When a grocery store puts something on it's shelves, the store itself bought it from the manufacturer. They have already made their money. On Amazon, manufacturers don't make money when the item is listed, they make it only if and when a customer buys the product.

It's way more complicated than that. Manufacturers pay stores to carry their products, feature their products in special places in stores, get forced to take buy back unsold product, get paid way later on invoices, etc etc.