Because the Gorelick wall was constructed to protect the foreign Chinagate information from the FBI, thus separating incriminating evidence from the criminals. 911 was just an unforeseen result of that policy because intelligence was too hamstrung to know about it.
That's one theory anyway.
Not so much a theory as an end result....
We know the result...
We know how it transpired...
We know who put those barriers in place....
Deducing the truth is pretty simple...it's not rocket science...heh..it's political science....practiced by mad scientists....
These people where more worried about covering their ass than ANYTHING else......period...
As I said...we know the resulting reality born of previous decisions...
Proving intent of malice and conspiracy in those decisions is another matter...