Because the real documents aren't incriminating.
Really, these forgeries aren't either. That's one aspect that held me back from accepting the fake theory until the technical aspects were drilled in my head and I got it (it took just a few hours--not days! LOL). They were designed to be spinnable.
Not in-of-themselves... but I believe they were supposed to be an "opening salvo" in an all out assault on W's Guard Service. Clearly, the Rats had a campaign ready to go, but they've been too stupid to call it off in light of these developments.
I suspect the people responsible for the forgery figured these documents might not get much scrutiny, but a document which read like "Today, I caught Lt Bush snorting cocaine in the mess hall. When I confronted him, he told me his daddy has connections and there was nothing I could do to stop him. He then spit on my face, and has been AWOL ever since..." would never pass the smell test.
Turns out that these more mild docs didn't either.