Probably where their antenna was located.

Here in NYC, almost all the stations had antennas on top of the Empire State Bldg. In the 1970s most of those antennas were re-located to the World Trade Center Towers. On September 11th I was only able to view Channel 2 (CBS) because they left their antenna on the Empire State Bldg. The other channels rushed to find alternate places from which to broadcast (and many didn't want to go to the Empire State in case it would be another target in the immediate future).

Now, with cable, that's all moot.