The 737 max is a great example of the rut we are in. In order to put more efficient engines on they needed more ground clearance. This has been the issue with 737 forever and why they have that odd flat scoop on the bottom of the engines. That isn't great for efficiency. It is because they can't redesign the wing without years long recertification. So, yet again, instead of redesigning the airframe to optimally place the engines they pushed them forward impacting the cg of the aircraft and requiring them to hack systems into the aircraft that countered for the reduced forward cg. Then, because they again didn't want to go through the recertification nightmare, they claimed no new training on the aircraft was needed. This led to pilots not knowing how to handle when the systems added failed. The root cause of the hacky design and missing training was avoiding a years long certification process that would have made it cost prohibitive to create an aircraft with more efficient engines. This is a minor change compared to building in really innovative new features.

To your argument of (paraphrase here) 'it is good enough why innovate'. I flat out reject that argument. Horse and buggy were good enough. The telegraph was good enough. We only needed 1 mb of memory because it was good enough. We are missing so much right now. We potentially could have small, efficient, point to point air taxi service for the average person, completely dismantling the massive, and horrible to deal with for people, hub and spoke system. Travel could get so much better and cheaper, but instead we have the 737 max. An incremental change on a decades old design because real innovation is lacking in the industry.