I’ve had more time stowing ships than aircraft but I know that similar principles apply, i.e. when unsecured cargo starts shifting it a) tends to go very quickly, b) it will always be in the wrong direction and c) the timing will be the most inconvenient.
So cg/nosewheel trim sensors would have been of little use if the pallets/containers were stowed correctly for cg but, unsecured, decided to go aft at rotation. There would be zilch warning.
411’s comment re the unlikelihood of there being empty spaces in the hold is apropos but it’s informed speculation; it doesn’t necessarily mean that there were no empty slots aft. There could be all sorts of reasons - a need for containers for the next flight and thus no empty repositionings for that particular flight. It could be a red herring but then again, maybe not. Icarus's posting on page 4 of this thread refers to an announcement from the airline that the tailscrape was attributed to improper stowage.