The reason here would be due to the implication the CIA may be involved. The CIA's charter (is supposed to) specifically prohibit domestic activity.

Facebook is in PRISM and a myriad of other government programs - everything that is posted, uploaded or chatted there is tagged, filtered and alerted for activity that the US government may deem dangerous or may want to pursue for other reasons (DEA, aggregate understanding and persuasion/'engagement').

Agreed broadly that this wouldn't be completely new news (were it to be confirmed). Technical details and confirmation do help citizens to understand that surveillance/'bulk collection' is alive and well.