Anyone know if this was really due to the fear these glitches will occur again in the future or that the cost really didnt justify the benefit?

I am not on many flights where the deboard/board is the critical path of the turnaround process. There are many other things that usually get in the way! If they were add that part of the equation into their formulas (percentage of flights where limiting turnaround factor was board-deboard), I think they would have found it doesn't pay and maybe thats the conclusion they came to.