|“||... Surely you know the story, that both glyphs and letters came from the Dawnsingers?||”|
|“||... Some think these chambers might have been cut by the Dawnsingers themselves.||”|
–Explained to Shallan by a master-servant about the Palanaeum
Shallan: "What about the Dawnsingers? ... Couldn't they have created it?"
Kabsal: "That isn't the kind of thing the Dawnsingers did. They were healers, kindly spren sent by the Almighty to care for humans once we were forced out of the Tranquiline Halls." 
Dawnsingers being kindly spren, may be misleading. So far it does not appear that in the past spren were in abundance the way they are now. This might be an interpretation or alteration by Vorinism.
A. There are various levels of Cosmere awareness.