When I see cockpit videos, the pilots tell each other what they do / run checklists together... Does the MCAS do the same, i.e. announce "stall risk detected, increasing stabilizer trim by 2.5 degree to xx degree"?
Inattention to autopilot modes has killed before. So much focus is put on pilots recognizing and confirming flight mode annunciator mode changes (such as change of autopilot or autothrottle state) has been put into place to stop that kind of accident.
The lack of feedback from the MCAS system is probably the killer here.
How am I supposed to know that MCAS is operating, and how do I know when to hit trim cutoff switches to override it? You don't want to ever be asking "what the heck is the airplane doing now?". Watching the trim wheel to check if it's spinning nose down all the time isn't going to work.
The Lion Air pilots were not even aware of the existence of the MCAS system, because Boeing at the time did not include any information about it in its manuals.
The behavior would be similar to runaway stabilizers, though, for which B737 pilots have memory items to perform (turn off the trim). This would have solved that problem. However, several other warnings and alerts, like stick shaker, might have been going off at the same time, making the situation chaotic and problems hard to diagnose.
An additional problem is that if it fails (the MCAS) the airplane is low, in full thrust during take-off and the pilots have zero room for error as the airplane is trying to dive into the ground (as in the LionAir flight).