Relationships between major airlines & Airbus (with their actual new model of a plane) were going too smoothly for Boeing’s taste. That was the crux of the matter.
How Boeing Tried to Kill a Great Airplane—and Got Outplayed
https://businessalabama.com/the-daily-beast-how-boeing-tried-to-kill-a-great-airplane-and-got-outplayed/
Boeing Was ‘Go, Go, Go’ to Beat Airbus With the 737 Max
https://www.nytimes.com/2019/03/23/business/boeing-737-max-crash.html
Please compare A220 sales to 737Max sales ...