I guess the question is why announce it they way they did during briefing. It should have be done discretely and quietly.
I’d say the press conference, which was unscheduled, and added at the last minute was just for the purpose of dropping this bomb. It was done for maximum effect and I believe is part of the cleansing of the deep state stables.
As a tactic this announcement was very effective. The MSM, and the Left are all reeling, dissembling, spinning and in their disarray they are unguarded in their speech further discrediting themselves. Masterfully done.
Not a damn thing will change cuz the FBI and CIA leaks like crazy.