The problem is S3 is just a lexicographically ordered key value store with (what I suspect is) key-range partitions[1] for the key part and Reed-Solomon encoded blobs for the value part. In other words, it’s a glorified NoSQL database with no semantics that you’d typically expect of a file system, and therefore repeated writes are slow because any modification to an object involves writing a new version of the key along with its new object.

[1] https://martinfowler.com/articles/patterns-of-distributed-sy...