Because I don't think that's the point of the article, which is just a commentary about how AI labs are marketing the effectiveness of their services by using terms like "8x more code per quarter" like that's an obvious good thing (which it isn't).

If you want a more in depth explanation, go look for interviews with devs who were already super-productive before LLMs and now came around to using them everyday.

If you read the paragraph, then why did you just ask "why?" instead of expressing your opinion about the explanation given in that paragraph?