On the contrary, Amazon could have become profitable on demand. They were just investing heavily into physical infrastructure back-to-back and if they ever wanted to slow down or stop, they'd be default alive.
Walmart back in the 80s investd heavily into physical infrastructure back to back - building new stores, their own trucks fleet. The first retailer with its own satellite communication system. There was never a question about Walmart going bankrupt.
I spent a couple of years in Amazon retail finance. The vendors were incentivized to sell as much as possible, under cost if that helps. Part of my job as financial analyst was to "convince" them it is a bad idea to sell under cost. Very hard and stressful work.
Isn't this "losing money on each sale but making it up in volume"? Sounds like I heard that before and it did not turn out well.