The difference is that Amazon had no profits in the early days because they poured money into improving their supply chain not selling products at a loss as a strategy. Drop shopping isn't the same as building your own supply chain out. There is no strategic advantage to be had placing orders with a drop ship network.

Amazon has no profits but bountiful cash flows. They make money on the margin when you buy something, they just invest it back into the business.

The well-known reason behind that is because of Amazon's capex, not because Amazon is losing money on reselling inventory.