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I agree with your explanation. In my post I implicitly suggested an intentional conspiracy, but that was poor wording/tone more than a reflection of what I think.
I don't think anyone who invokes "the Cathedral", myself included, believes that it's a literal conspiracy making coordinated efforts to deceive the public. A description by Zero HP Lovecraft: "the cathedral is a decentralized conspiracy of leftward-ratcheting signal wars, in which everyone defects against decency and morality in order to become holier than their neighbor". "Leftward ratcheting signal war" seems like a solid description of the process you described.
I've previously been skeptical that a "decentralized conspiracy" could be effective and converge on a single narrative, if it wasn't approximately the truth. I'm seeing that open letter as an example of how it can happen.