It was that they were too large and there wasn’t enough underwing clearance to mount them under the wing. They mounted them in front of the wing. This moved the center of thrust further forward relative to the center of lift. Increase the chance of a stall. To counter this, they added a new anti stall system that they didn’t tell anyone about. The in cockpit warning light was not standard and the system only pulled flight data from one sensor.

So in the event of a system failure the pilots didn’t know about it, didn’t know how to turn it off and it had a single point of failure. The only way this got past the FAA was they did an “in house certification” and didn’t tell the FAA. I can’t stress how bad this was for the PR of both Boeing and the FAA.

So basically they did a bad software fix to fix a hardware issue. One that they intentionally created because it was too costly to do the engineering and airworthiness certification required to put the engine in the correct place. And didn’t tell anyone about the new system because that would have required pilots to have additional training for the new Max plane. Which the airline with the largest 737 fleet didn’t want to have to pay for.

Yeah even though they “fixed” the software fundamentally the engines are in the wrong spot. I won’t ever fly on one and I work for an airline…