I was there at the time - seem to vaguely remember it was because they could! Probably a record having all four Mk3 Phase 3 Shacks serviceable at the same time.
Did one trip on them shortly after they arrived at Sharjah. With four turning and two burning it still took 20 nauticals to reach 3000 ft! Goodness knows how a Mk 2 or a non Phase 3 Mk 3 would have performed.