I am no expert, but I remember the main culprit was that Boeing had insisted no further training is required for pilots to avoid some sort of expensive recertification.
Weakness of pilots was the direct result of this. Pilots having experience with previous 737 planes were told in no uncertain terms that they can fly this new plane the exact same as the previous one and no further training or testing is required or even available. They did just that, but actions which would have saved the plane in previous generations ensured its crash in the MAX generation.
And Boeing had the audacity of blaming the pilots when they inevitably died in crashes.
> In vivid detail, the documentary pieces together what Boeing knew about the potential for disaster with the 737 Max and when the company knew it. Pasternak says in the film that in 2012, a “Boeing test pilot was flying the MAX in a flight simulator and trying to respond to an activation of MCAS, and that resulted in what he described as a catastrophic event. It showed that if that had been in real life, he [could] have lost the airplane. They realize from that moment on, even a Boeing test pilot may have trouble responding to MCAS.”
> Yet internal communications explored in the film show that Boeing was determined to maintain the status quo: avoiding potential scrutiny by the Federal Aviation Administration that would add costs; keeping new simulator training for pilots to a minimum; and even requesting that MCAS be removed from pilot training manuals.
https://www.pbs.org/wgbh/frontline/article/video-clip-boeing...