In ATLA there was never a concept of Harmonic Convergence and Avatar Wan and Raava and stuff. That's why there are a lot of plot holes. I found another one where:
In the lover's Cave episode the scripture on the wall read that Oma and Shu were the first earthbenders and that they learned earthbending from the Badger Moles. But in LoK people who lived on the earth lion turtle already earthbend and when they left many were already earthbenders.
SO the original idea was probably to have 1000s of Avatars over the course 10s of 1000s of years. But they shrunk it down to 10,000 years o have the avatar. And yes it doesn't add up because every time we see all the Avatars like in the Winter Solstice pt 2, LoK Season 1 finale Endgame and in the Southern Air Temple, we see thousands of avatars, more than the eye could see at once. Add it doesn't make sense since every avatar would live to, not an average of 50 years but an average of about 60. Kyoshi lived the longest for 230, Kuruk the shortest for 33, Aang 165, Roku about 90, Wan looked 90 at death, Yangchen pretty young in her middle ages unless the air nomads have some special water to make you look younger, Szeto looked pretty young he had black hair but that could be dyed. but still, the average is about 60 years. That only makes 166 avatars in 10,000 years. It just doesn't add up. And I know what you are gonna say, yes they could die young, but whatever an avatar looks like when Korra and Aang had visions, that's the age they died at and that's what they looked like when they died.
