It's a pretty abstract concept, to be sure
You're essentially fusing parts to both your body and to each other. Detachment is not a completely non-destructive process, so reattachment without further modification is not possible. That and when you reattach it could be connecting in a slightly different way, or location, or integrating with other parts. It's not at all a truly modular and reusable system.
When you learn the nature of what Cogmind really is, this will make a little more sense, too.