Thanks Ken makes a lot of sense.
I had thought that perhaps a specially reinforced floor might have been installed in a cargo 747, but I can see how you explanation is lighter and still fit for purpose.
That transcript is very sobering. It is almost as if they almost realised how dangerous what they may have seen was, but some complacency perhaps did not lead to enough caution over the risks.
Maybe the load was infact re-secured after their discussion, but perhaps by then some of the straps had been critically weakened.