The B-737 has very short undercarriages and, therefore, low ground clearance. That made sense when it was powered by low-bypass turbofans, which has small diameter and were of cigar shape. After high-bypass turbofans, which offerred superior fuel consumption, came along Boeing had to move the positions of the engines to solve the clearance problem and that affected flight stability.

Until it came to MAX8, the high thrust, large diameter and position of the engines rendered the plane naturally unstable and Boeing wanted to solve the problem with MCAS to make it artificially stable-- instead of designing and building a new plane.

If and when MCAS fails to work properly, the plane becomes suicidal. The rest is history.