I just can’t help but wonder if the lifting and landing calls from these two aircraft were made simultaneously, thus neither heard the others call. “Two at once” does happen occasionally and would explain the apparent lack of directional scanning.
The thing with that is, you have to close the loop. So if I make a call and don't hear a reply, I would call again. Also, most times the pilot would be aware of a 'two in together' situation by the sidetone, and again, make another call. It seems that wasn't the case here, for some reason which will hopefully emerge in the investigation.