Transhumanity has many offspring. Engineered smart animals, AIs and AGIs, loose beta and delta forks, but fewer and fewer children. Fertility rates among transhumans are low. It is expensive to bear and raise a child, requiring space, time, and bodies that not everyone has access to. It is only natural to want the best for your child, and the plasticity of children's brains and bodies take very rapidly and naturally to augmentation. The lost generation were only the beginning.
The agōgē promises to raise Ultimates with an ideological purity and an adoption of transhuman technology and capability that overshadows their old-fashioned seniors. To the members of an ideology prizing self-improvement above all, to become obsolete and irrelevant is worse than death.
This is the precociousness problem: any children raised to the fullest transhuman potential will very thoroughly surpass their parents. Those children will create and raise their children better than their parents could. Then their children will overcome them, and so on. It is a long term singularity, carried out over generations. Bio-conservatives fear an inevitable specialization leading to exhumanism, hyperelites fear the loss of their position, most others fear irrelevance.