Because it is meandering, lacks a clear focus and organization, falls down tangents, etc.
People who are excellent writers within a professional system where (1) they aren't writing about themselves, and (2) have the support of professional editors, etc., before the public sees the work, often have much lower quality without #2 or when the context is far from #1, such as writing about personal incidents that are highly charged. And most especially when both of those occur at the same time.
And I don't claim his writing in the general sense is poor quality, I say that the four-part epic on this incident is poorly written.
Or maybe it intends more to graphically convey the flow of consciousness that results from extreme indignation more than to inform effectively about the author's side of events, in which case it's a masterpiece of written art. “Poorly written” definitely makes an assumption of purpose that may not be warranted: as a show-not-tell feelings piece it is tremendously effective.