BW mix disabled when BW Camera Profiles are selected

When a Color Camera Profile is selected, the user has full access to the HSL menu. But for BW Camera Profiles the BW mix is disabled.  For some brands (Fuji, Nikon) a dedicated ‘BW + filter’ profile is provided (e.g. Acros, Acros +Y, Accros +R) but not for my Panasonic Lumix files.

The only method to tweak the color response  and emulate a contrast filter is to use the Adobe Monochrome profile. What is the rational behind disabling the BW mix ?