My memory is that if Amazon had been happy with just books and bookish stuff they would've turned a profit much sooner. A smaller, and possibly short lived, profit...but sooner.
Profit is a pretty misleading metric. Amazon had enough income to exceed their operating expenses for quite a while. This is the intuitive definition of profit, but not what appears on a balance sheet. They were taking all of that money, using it as collateral to borrow more, and then investing all of that in growing their business. That meant that they didn't make a profit, but only because anything that would have been profit was ploughed straight back into the business. They were also very willing to shift markets. They created a cloud offering because they had to over-provision in their data centres to cope with spikes in demand and realised that they could sell some of this excess capacity. This turned out to be so lucrative that they poured all of the profits from their retail arm into expanding it for years. They did the same thing with the Kindle.