If they simply implicated an "APT" in wrongdoing, they would have released it, as it would have been unremarkable and fit neatly within the Overton window of hissing-chinese spys justifying an even more expansive national security apparatus and general anti-sino sentiments among the ruling class in Washington.

This leads me to two possible, non-exclusive outcomes: the links to China are tenuous, and the attribution is flimsy (e.g., they accessed a machine at 9 am Beijing time!); or the report implicates the system itself as unauditable by design, which was bound to happen given the design of the intercept tools.