When Airbus released the A320neo , Boeing needed to get a comparable plane out ASAP or else cede several (tens of even) thousands of plane sales to Airbus over

When Airbus released the A320neo , Boeing needed to get a comparable plane out ASAP or else cede several (tens of even) thousands of plane sales to Airbus over the next decade. There wasn't the time to design a whole new plane, so they pushed the design of the 1960s era 373 as far as they could go. The details of the "risky" changes to accommodate the larger engines (that significantly changed the planes aerodynamic profile) and attempts to compensate for that with MCAS are already documented elsewhere. Keep in mind, there is a gold rush for new airlines right now. Africa/India/Asia are developing and are requiring thousands of planes to fill the demand (it's no coincidence Africa and Asia is where these new planes ended up crashing). If Airbus gobbled them up, they'd likely be airbus customers forever, as mixing plane types is more expensive for airlines.