CSMA/CD exists specifically to detect and handle collisions that occur when two stations transmit simultaneously on a shared (half-duplex) medium.

In a full-duplex switched Ethernet, each device has a dedicated, point-to-point link to the switch, with separate physical send and receive paths (e.g. separate wire pairs). Because:

1. Each link is used by only one device (not shared among multiple stations), collisions between different devices cannot occur on that link.
2. Since the send and receive channels are physically separate, a device can transmit and receive at the same time without its own outgoing signal interfering with incoming data.

Since the fundamental precondition for a collision (multiple stations contending for the same shared channel at the same time) simply doesn't exist in this topology, CSMA/CD's collision detection and backoff mechanism becomes unnecessary and is disabled in full-duplex mode.