The number of people who have killed heroic Garrosh is still minimal. Less than 2% of all guilds that have killed at least one normal mode, according to WoWProgress, which presumably means less than 1% of all guilds that raid at all. So there's still stuff to do. Considering that the heroic version of the fight includes locations and mechanics not seen on lower difficulties, very few people have actually seen all the content that's currently available.