wheelsright:
However, the question is why substantial disagreement between sensors was not regarded as an important factor in disabling MCAS automatically?
This is the question which Boeing needs to answer.
Boeing has now revealed that the MAX had a system which compared the values supplied by the Left and Right AoA sensors. This system was supposed to flag an alert to the crew when the disagreement between the sensor values exceeded, presumably a set threshold. This AoA disagree alert was not actually implemented due to an error/oversight which the company discovered in 2017.
Thus, it seems the MAX had a means of checking the validity of AoA sensor values from day one. I cannot comprehend why this AoA disagree signal was not used by the MCAS system to inhibit nose-down trim inputs to the HS for as long as the AoA disagree signal=TRUE. Had this been done, it is unlikely the Lion Air and Ethiopian crashes would have occurred.