When a hair is extracted with FUE, why doesn’t it grow back? I mean, couldn’t you just extract the greater part of the follicle, and leave a small portion still in the dermis, and it could generate two hair, like follicular multiplication?
When performing the FUE procedure, you may potentially transect the follicle, thereby damaging it and causing the hair to not grow. The other possibility is that if the follicle is left behind without damage, then it might regrow. What you are postulating has been a study that was done by many people and published in medical journals (an interesting article that addresses this is: “Cloned” Hairlines: The Use of Bisected Hair Follicles to Create Finer Hairlines).
Basically, one hair will not make more than one hair. When a hair is cut in two, one part dies and the other part may grow, but if it does it is often thinner than it was before the damage was done.