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.