My two cents...
As I like to group things in threes, my explanation for Amazon's success is that they had better leadership principles, better execution ability, and a better theory about the future (all business strategies make an implicit or explicit claim about what the future will look like) than any direct or indirect competitor. Could at least some competitor have been better than them at one of those? Perhaps. I don't think any competitor matched them along all three of those dimensions.
Amazon's '97 letter to shareholders gives you a taste as to their theory of the future. Everyone already knows about their ability to execute. Most already know their leadership principles. From an anthropological perspective, I find it relatively insightful to revist them from time to time. Here they are:
(1) Customer obsession.
(2) Ownership.
(3) Invent and simplify.
(4) Leaders are right, a lot.
(5) Learn and be curious.
(6) Hire and develop the best.
(7) Insist on the highest standards.
(8) Think big.
(9) Bias for action.
(10) Frugality.
(11) Earn trust.
(12) Dive deep.
(13) Have backbone; disagree and commit.
(14) Deliver results.
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To speculate even further... suppose someone were to ask me, "Distill the insights Bezos & Co. made into a single element so that I can understand what Amazon is. What is that one thing or what is Amazon really all about?" What would I say?
Benedict Evans would talk about a machine that makes more of itself.
Scott Galloway would talk about storytelling and its relation to cheap capital.
Ben Thompson would talk about an entity with multiple moats that takes a cut of all economic activity (or maybe just describe some version of an aggregator).
Many others would talk about the virtuous cycle of lower prices --> more customers --> etc.
I would say:
"Warren Buffet had a breakthrough insight - the competitive moat - in the 60's that ended up dominating business thinking up to the present (and will continue to be important/fundamental into the future). Bezos & Co. made an insight of similar importance. Namely, the actual value of an asset truly does outstrip your present understanding of its value, and outstrips your present understanding in a very significant way.
No breakthrough insight is sui generis, as it is constructed using already existing conceptual elements. Buffet's moat was there in the financial statements, and already intuited in a vague way by successful investors and managers before the 60's. The same can be said about Bezos & Co. It's a truism of managerial economics that the point of business is to move under-valued assets into higher-valued uses. Amazon both took this to heart (they internalized it) and they recognized that the true extent to which an assets value outstrips your present perception of said assets value, was an order of magnitude greater than anyone thought before."