I would think because as all but one flight had approached Antarctica in brilliantly clear conditions and the final letdown was entirely VFR with no need for instrument cloud break procedures.
There was report from the ice about low flying commercial aircraft, why nothing was done about it is probably because, even though they broke rules or regulations, one would expect senior captains to not do anything that would endanger the flight.
The critical part of the observation Brilliantly clear conditions.