If they had landed later in the day during daylight hours, they probably would have landed on the runway. The localizer and approach lights were NOT on at the time.
From the ntsb report:
The flight was cleared to land on runway 27R but instead
landed on taxiway M, which is situated immediately to the
north and parallel to runway 27R. The runway lights for 27R
were illuminated; the localizer and approach lights for 27R
were not turned on.