Remember this patent from 2001?
This was when Boeing was set on a new aircraft design and not furthering the 737 design.
Twin Aisle small airplane.
https://patents.google.com/patent/US6834833B2/en (an NMA?)
Have to love the bench seats!
quite unlike the A300 series?
Then A320neo happened and sold 4500 before even taking flight.
Boeing's response was to scrap the new design (which would have been operational by now) and stretch the 737 to the MAX.
Just as the NG was a response to the A320, (the A320 was 33% more efficient than the current B733) the MAX is a quick response to the sales of the neo series.
Not to mention the lack of a Boeing model to counter the A321/A321neo series.
Meanwhile, a new aircraft, the Boeing NMA is just a twinkle in their eyes...but the patent is still active!