The EOS 6D is a product that Canon seems to be aiming at "first time" full frame DSLR users. To keep the price down and differentiate it from the 5D MkIII they've made some conscious choices about what features to include and what features to leave off.

The EOS 6D offers a silent, low vibration shooting mode. By slowing down and muting the shutter and mirror reflex action, the camera is capable of handheld, virtually imperceptible operation for discrete shooting in more situations.