Airlines say they found loose parts in door panels during inspections of Boeing 737 Max 9 jets

There’s a long list of reasons:

• training pilots to change planes
• training maintenance teams
• changing procurement practices
• adapt supply chain
• etc
• and then on the bottom, 2 of the most important ones: cost control (maximize profits) and comfort

Boeing advertises the 737 Max by saying that it works just like the old 737 so you don’t need to retrain your pilots and save money. The issue a few years ago with that is that these planes are not 737 so when some new issue happens the pilots don’t know how to deal.

The cost of retraining their pilots would bite into their profits.