... and do the corrective action straight away. It only took a few seconds delay for the situation to develop beyond what the simple remedy covered.
What I conclude happened - the stuck sensor caused a sudden stick shaker and stall warning, masking the sound of the trim actuating. The airplane felt out of trim, so the pilot applied trim manually, setting the badly programmed system up to push the plane way out of trim.
MCAS was programmed to only apply a little downward trim, but that reset if the pilot applied manual trim. So MCAS trimmed 3 down, pilot applies a bit of up trim, then pauses to see if he has done enough. MCAS puts in another 3 (really fast), the pilot trims up again, maybe 1. MCAS puts in another 3, etc. Soon you are way out of trim.
So all of this leads to a delay in identifying a trim system failure, and so a delay in applying the cut out switches, while the plane speed gets out of hand (Note, you are hoping they'll pull the throttles back while they are still hearing a stall warning!). Pilots overworked until the situation is beyond their training, and then you are relying their skills as test pilots.