Because never before had a newly ascended World Tree sent their Chroniclers away without taking the time to assimilate the social knowledge that the elven tribes that lived with the Tree carried.
The Yggdrasill kept for himself only what was related to magic and the ways to nurture magical resources.
There was so much to know that even the mighty Tree could barely contain the fruits of the sheer magical research that their predecessors had accumulated from times that long preceded even the Guardians.
Never before had a young Yggdrasill spread their consciousness through so many Chroniclers at the same time while putting the lives of their emissaries at risk. In the rush to leave the Fringe once and for all, the new World Tree had bitten more than they could chew.