...a 737 has a 2 pilot crew. 1 flying the aircraft, the other handling the RT. A "late landing clearance" can be difficult because you (the ATCO) broadcast your "instruction" to 1 pilot, yet the action required is by the other pilot.
Very good point there, NoD. The person who read back the instruction was not the one doing the landing - if the landing pilot was concentrating hard, hearing is one of the first senses that get dulled under increasing workload. Maybe the PM assumed the PF had understood the GA call and was going to action it, and/or there was a bit of CRM breakdown in that the PM did not intervene when it became obvious that a landing was going to take place anyway?