Basically, the MAX has sold well for the reason that Microsoft Office has sold well. It had a set of features that airlines needed even if it was kind of junk o

Basically, the MAX has sold well for the reason that Microsoft Office has sold well. It had a set of features that airlines needed even if it was kind of junk overall; it was "backward compatible" with earlier 737 models and it saved a lot of gas compared to them. The backward compatibility was key since it save a lot of further money that would otherwise be needed for retraining and retesting (Airbus had a gas saving plane that would require retrain and this was the "killer app" versus that).