But what has been happening in Chicago/Seattle over the last few years? It hasn't been a secret that the A321NEO/LR was eating the -9's lunch. Any reasonable person should have reached that conclusion by like 2014 at the latest.
Boeing was frozen into inaction by internal (two externally peer reviewed) inquests held into the financial under-performance of three new models, compounded by heavy discounting on the outgoing 777 family.
The 737 (and 767) has been the bread winner, with 'achieved' prices inflated by full Airbus orders, engine issues, long waits for new customers, and premium pricing/high margins.
The A32X CEO and NEO families enjoy the fattest margins in the industry, and the A321 is the pinnacle.
As the Airbus order book starts to taper, they have far more margin to play with than Boeing. I don't know what profit sensitivity analysis Boeing has or will perform on the latest MAX model, but.... If the latest 737 doesn't deliver the promised financial results, their Board's willingness (and ability) to support new models will likely be impaired for the next decade.