On some systems, the camera won’t perform focus-confirmation calculations unless it detects that a lens is attached. The chip in certain Canon/Nikon adapters acts like a basic electronic lens ID so the body recognizes “a lens is mounted” and enables that behavior.

The chip may also pass simple lens-related data such as focal length, aperture, or calibration/micro-adjustment information, which can help the camera’s confirmation logic work more reliably.

By contrast, some Pentax bodies supported focus confirmation with older manual lenses natively through the mount/body design, so no extra electronics were needed in the adapter or lens.

A likely design reason is system compatibility: if the camera only enables the feature for electronically recognized lenses, the manufacturer doesn’t have to guarantee support for every older manual lens. In short, the AF-confirmation chip is mainly there to make the camera think an electronic lens is attached, and sometimes to provide basic data that improves confirmation accuracy.