The main problem with the 737 is really just that it's old, and at every single turn Boeing has chosen to make incremental updates instead of redesigning it. A

The main problem with the 737 is really just that it's old, and at every single turn Boeing has chosen to make incremental updates instead of redesigning it. An issue like MCAS would be much less likely if the aircraft was designed to be fully fly-by-wire - but a fully fly-by-wire single-aisle would have to be recertified from scratch. The problem with jetliner manufacturing is that you kind of have to bet the company on every single new model you release, just because the process of designing a new plane is so cumbersome and difficult that you can't really afford to be doing it very often.