The 737 MAX is the symptom.
The root cause is systemic failure.
Normalisation of Deviance.
The root cause believe it or not was the 787. Boeing admitted that they should have just built the whole thing in house and got it right the first time. Instead they outsourced it had a laundry list of problems which flowed into production delays.
Plan A was to make the 737 Max a new design using 787 technology but that became so delayed they were then forced to cobble the 737 back together with even bigger engines to be able to compete with the A320 and now here we are with a looming disaster. Even if the Max gets going again there might be so much negative publicity that people refuse to fly on it. That will be Boeing's and the Airlines worst nightmare.