Why do game companies always keep release dates secret?

[Dolla Dolla]

I work in an industry dependant on precise dates, and let me tell you, even those are up for changing. There's no telling when a wrench is thrown into development, or QA, or a big decision from the people who make the big decisions. It is much safer to give a guesstimate to the public, while behind closed doors they have specific dates they target, but may not always hit.