It is/was in peoples mind for years that frost is not viable and just for PvP.
While this has changed, the minds of the People are still a bit behind. Same as with Paladins in BC. If you were a Paladin and telling the People that you are tanking ,they went like "Wut? LOL dude Paladin is meant to heal, as he cant tank and cant do DMG."
It will take some time for this "Frost is for PVP but not for DMG" idea to vanish out of peoples minds.