Because there are a bajillion options. Those 3 books are all 600+ page paperbacks that cover Rand, visions of the AoL, the Aiel & their fancy Rhuidean, a cache of terangreal that went who knows were, Forsaken, Tinkers, and at least 4 nations.

There's a list on dragonmount's forum that is full of (apparently) people's suggestions. You can check it out, but it's not organized terribly well.