One of the interesting dichotomies of the rogue class is use of Stealth. Stealth, and by extension, surprise, is paramount to rogue PvP and most of the rogue leveling experience. In these situations, the optimal strategy is to use an opener to gain an early advantage over your foe. Ambush, Cheap Shot, and Garrote immediately set the pace of the encounter. When fights only last a few brief seconds, Stealth tips that tenuous balance in our favor.
Once raiding enters the picture, the value of Stealth drops to near zero. Assassination rogues get a slight boost from using Garrote against a raid boss, but we're talking about less than a 1% difference. Combat rogues don't even bother using an opener at all -- all of the options are too weak. Subtlety rogues, who are designed around Stealth and openers, require the cooldown Shadow Dance to function. Stealth and its relationship with combat simply don't work in protracted battles.