A) The product hasn't even shipped yet. That may be an option or made into one in an early update.
B) There may be a technical limitation to disabling or rebinding it (e.g. without impacting either other buttons, or the behavior of actual keyboard buttons).
Currently the only way to influence it is to delete registry key
[-HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SurfaceHomeButton]
and kill all physical buttons completely.