That just means that you, I, and other knowledgeable people are not the target audience, and he intends for it to be read by people who do not have the context

That just means that you, I, and other knowledgeable people are not the target audience, and he intends for it to be read by people who do not have the context to disagree with his just-so story for why Plan 9 failed, which coincidentally includes a business principle. And my interpretation of his thesis boils down to: Don’t scratch your own itch. Fine. I have my own explanation for why Plan 9 failed, and there are lots of reasons you can invent, based on hindsight and your own biases.