Because their locations are or were undisclosed, and obviously not even everyone here has heard of them. They exist.

Edited in reply They are explicitly said to exist in Hollywood propaganda film Zero Dark Thirty (2013). No, this is not proof, although it is evidence. If the establishment wants us to believe they exist, is that not troubling enough?

FYI hollywood propaganda films aren't usually the best citations...

EDIT: spelling counts...

the fact that the movie made a splash within the security community for "saying too much" helps to give credence, as well.

Yeah, it's a movie, but the people who were upset about it being released were people in authority.

With Hollywood's ties to the US Government, it was probably a fake attempt to get their buddys' movie to sell better...

who knows. theories abound.

For the same reason the Gestapo were the official secrete police of the Nazi Germany. Abbreviation of Geheime Staatspolizei, "Secret State Police"

Or the US Secret Service...