The engineers had designed two redundant sensors into the jet, from the start. Every 737 Max has them. So they knew they needed redundancy. They also designed a way for pilots to switch off the automation.
But they had not finished the redundancy administration software at the time Boeing wanted to start shipping.
So they were ordered to issue a partial release, using only one, with the intent to upgrade it later.
And Boeing did not want to alter the pilot training process, since so many pilots are already 737-certified, this was a huge advantage for faster and lower cost adoption.
So those Ethiopian and Indonesian pilots had no knowledge of how to override the MCAS gone awry, even though a way had been engineered to do it.
To give the MCAS full authority over flight controls, in conflict with the pilot, in reliance on a single sensor ... this is insane. It is evidence of systemic problems in the architectural review process.
Passengers should never have flown for a single hour with that configuration.
This was a significant management error, owing to commercial pressure to compete urgently with airbus.
Moreover, the whole idea of an expensive angle of attack sensor, of which the jet has only two, is sort of ridiculous in modern day tech.
Every iPhone has a mems sensor capable of knowing the angle of attack with respect to earth ground.
These sensors are now tiny and cheap, and very precise. They could have had a hundred redundant sensors for less than one tenth the cost of just one expensive aerospace style sensor that has now failed twice in the last 5 months.
You could read that array of mems sensors and make decisions based on statistical probability. The odds of the majority of those 100 sensors being wrong is so low as to be absurd.
This was an avoidable problem. Those people did not need to die.
Btw - airbus too, has a similar two-sensor scheme like Boeing. This is an aersoace industry culture problem, where commercial tech has far outpaced them, and they stick to old techniques past where they make sense.
When Boeing had fire problems with their lithium ion batteries on the 787, it was found that they did not have basic thermal meltdown protection systems that are standard on every Tesla car.
We assume that the biggest players all do the smartest thing, but it is not so. Their size creates a kind of overconfident blindness, which only gets fixed after tragedy.