The Old Ones presented the dying wanderers with a choice, one that each of them had to make for themselves.
The one choice was to avoid further pain and to let their lives go – to move on to whatever is next, and take another life in a place far away from Earth to start over without all the suffering.
The other choice was to stay, and after death to be born again and again in the bodies of the young Earth races. Those who took this choice would struggle as the humans did, but when the time of the great change came, they would be allowed to remember who they were, and help to direct this world on its road to awakening.
For their own reasons, many took this last choice.