When I choose the BEACH ON mode (GROUND menu) to detect in the wet zone of the beach, the TRACKING mode is no longer available. Why is this?

The TRACKING mode is not available in BEACH ON mode because the PUMPING mode is much more effective and gives a more rational setting value.
On the beach, pumping (moving the coil up and down above the ground) gives a more precise measurement value than sweeping.
On the beach, pumping (moving the coil up and down above the ground) gives a more precise measurement value than sweeping.