Why? Mainly because it most clearly demonstrates the issue.
It's not clear to me, especially in light of the faux pas about CRU, just what issue that is. My intervention, as you will see if you refer to my original post, as well as pointing out that you had the wrong Man(n) (you had Jones) and taking issue with the hyperbolic attack on the statistical failings, such as they were, of the good Professor: was that the original hockey stick paper has long been superseded.
In any case, it is my (limited) understanding of Mann, Bradley & Hughes 1998, is that it is generally accepted both that better statistical methodology could have been applied; and that the methodology actually used contained identifiable mistakes (however minor they may have been). I believe Dr Mann himself concedes as much. "Really really bad," however, probably tends towards hyperbole.
If he knew what he was doing, then he was actively trying to deceive people, which is far worse.
That's a reading the "hide the decline" [of correlation between tree-ring and other proxy data relating to the sub-set of Russian trees after mid C20th, was that it?] comment might naturally lead someone to form. But really isn't it just the that the blow-tourch of criticism on this particular subject matter renders good-enough methodology not nearly good enough? Scepticism, where it is informed, is a great boon to science.