Hi,
Because it's one of the most difficult situations to reliably work out - as has been stated previously.
This is feasible, should be done long time ago and the approach used by Airbus SAS showed in the earlier mentioned paper from the Design group is IMHO an ERROR.
To diagnose UAS just by "System output" is DANGEROUS and a good example of K.I.C.S. (*)
This flatly contradicts any assertion that the systems were not providing the relevant information to the crew.
The System provided a lot of information including processed garbage. What you need is just FAST and PRECISE information.
...at least half the crew on the flight deck were well aware what the problem was.
A good man-machine interface could provide to 100% of the crew (including Capt) reliable information.
(*) Keep It Complex Stupid