Originally Posted by
huth
Garrisons weren't sharded, they were Scenarios. Sharding worked just fine in Tanaan. Problems happened when everybody, their dog, their dog's dog and their tapeworms each had to go into individual instances and completely overloaded the instance servers, which was compounded by there being a massive surge in active players around release.
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Because there was a crapton of players sitting in front of the garrisons. Questing also had issues since many big questlines had scenarios as capstones, that naturally also failed to load for most people.