it is because of NTZ.. what is NTZ?
NTZ (no-transgression zone) - A corridor of airspace of defined dimensions, located centrally between the two extended runway centrelines, where controller intervention is required to manoeuvre the non-blundering aircraft when the airspace is penetrated by an aircraft conducting a simultaneous approach to the adjacent parallel or near-parallel instrument runway.
In the context of independent parallel approaches, a corridor of airspace of defined dimensions located centrally between the two extended runway centerlines, where a penetration by an aircraft requires a controller intervention to maneuver any threatened aircraft on an adjacent approach. This is normally a 2000-ft (600 m) wide zone.
