You're absolutely right. Amazon was already a huge successful company when they began their microservices journey. Mr. Bezos is the only chief executive I know of who has knowingly applied Conway's Law[1] to corporate governance. Amazon's conversion to services is best understood as an hybrid managerial/engineering decision. This means that the microservices approach only makes sense as part of a larger organizational strategy. A small organization is almost always better off building a monolith, because while it's less efficient at scale, if the organization is successful enough for that to be a problem, it's also successful enough to be able to afford the rearchitecting, assuming competent leadership.
[1]https://en.wikipedia.org/wiki/Conway%27s_law