"Keep in mind that I'm not a full doctor, I only took a half-load of med courses for three years. Our way of body-modification is a lot less finessed than yours. The going theory is that shapers unconsciously support their add-ons in ways that baseline humans can't. Shapers will grow capillaries in a new appendage all on their own, they generate their own skin and sweat glands, their new bones grow marrow without grafting, their minds more easily learn how to control new muscles, and so on. Non-shapers do none of these things, so it's all manually created, and it's too easy to miss something and end up with a defective body."