Uh, because the '10 times more productive programmer' is folklore, at best? It may be true, but there's not much hard empiricism behind the claim. See https://www.readability.com/articles/5egv0hme?legacy_bookmar.... Cook admits it's hard to tell who's more 'productive'. Well, if it's hard to tell, why take that claim for granted in the first place? I am sure Cook and everyone else likes to think they're the 10x programmer, however.