Because Sometimes More is More
Foreskin can be divided into two portions: the inner foreskin and outer foreskin.
Inner foreskin is the portion of it that directly touches the glans (at least when the penis is flaccid), and is composed of a different type of skin. Inner foreskin is thinner, pinker, and much more sensitive than outer foreskin. It’s where the ridged band and frenulum are, and overall it has many more nerve endings than the outer foreskin. Circumcision removes a varying amount of inner foreskin- some people lose hardly any of it, some lose much of it, and some are left with literally not a piece of it.
Outer foreskin is the portion that goes over the head but doesn’t directly touch it; that is, it’s the part that touches one’s clothing/the air if naked. Outer foreskin is basically the same as regular shaft skin, it’s just called foreskin because it’s located over the glans.
In foreskin restoration, if any inner foreskin remains it’s important to ensure that both regions of foreskin are given tension to ensure equal growth. This can be accomplished through specific manual tugging exercises, or through device that are intended to tension both the inner and outer foreskin.
In my mind this one of the most elusive things to understand about the foreskin (next to the frenulum), and a source of variability in terms of which parts of the penis are removed during a circumcision.