My thought was that his personalized horcrux spell tied whoever it was used upon to the horcrux network he built.
Therefore, by using it on Hermione, instead of having two parallel horcrux immortals, Hermione’s mind was connected to his network, and he was disconnected.
This was not something he had ever examined in detail, because it never occurred to him to spread his horcrux method around before.
My thought was that his personalized horcrux spell tied whoever it was used upon to the horcrux network he built.
Therefore, by using it on Hermione, instead of having two parallel horcrux immortals, Hermione’s mind was connected to his network, and he was disconnected.
This was not something he had ever examined in detail, because it never occurred to him to spread his horcrux method around before.