This changed the handling characteristics of the aircraft. Worse, the nacelles generate their own lift at high angles of attack. With the engines farther forward of the aircraft center of gravity, the engines generate an upward pitching moment. To make matters worse, it's a positive feedback system -- the higher the angle of attack, the more lift the nacelles generate pitching the aircraft higher which generates more lift on the nacelles, etc. I've read this positive feedback pitch-up can happen very quickly, hence the need for automation (i.e., MCAS) to counter the effect very quickly.
A reader comment on the EE Times article links to an interesting analysis by Gregory Travis at Boeing 7373MAX. Mr. Travis confirms what I've read, but adds an interesting financial analysis. He says these handling changes should have required this to be classified as an entirely new airframe requiring complete FAA certification, a process that would take years and costs untold millions of dollars. He says that Boeing created the fiction that the MAX would have the flight characteristics of other 737 types and not require complete new certification or pilot retraining.
He writes that FINANCIAL considerations beat out SAFETY considerations on the MAX.
In my opinion, all of this can be laid at the feet of the extreme environmental lobby over the past decades. They have forced governments to adopt fuel economy standards and emission standards for cars, trucks, planes, ships...any transportation system. It was inevitable that the endless quest for higher fuel economy was going to reach diminishing returns and probably result in lives lost.
The automobile analog is the continued weight reduction of cars which led to more severe, more deadly crashes and higher loss of life.
Nice summary. Boeing is going to be writing some checks to “victim” families.