This will take an examination of culture at Boeing, particularly before and after 1997 to see the changes. Diane Vaughan examined NASA after the Challenger accident and issued "The Challenger Launch Decision: High Risk Technology, Culture and Deviance at NASA" in 1997, (revised 2016). The examination led to changes but not before Columbia was lost. I believe there is something similar here. Hopefully there is someone with the capacity, time and energy to do so because the question does at least need asking with regard to both organizations, (FAA & Boeing themselves, and also the relationship between the two).
777 was the last program I worked on at Boeing where I felt they did everything pretty much as it should be done. "Working Together" was the motto and that meant not just consulting with customers, but coordinating internally by having 'design/build'' teams working with each other all the way rather than emerging from their individual tunnels at the end of the process to find miscommunications and things that didn't work together properly. After that program, Boeing dismantled their traditional design matrix organizations which served as checks and balances on each other, but required lots of staff. Later programs seemed to have lost that magic and each follow-on project was mandated to have a faster and cheaper design/build/test/certify cycle than the previous one. Most of the low hanging wasteful effort was eliminated long ago and it was value added activities that started being cut. I felt that trend culminated on the Max program which kicked off with a misguided dream by program leadership that they might actually be able to eliminate flight testing altogether because prediction methods and computational models were so accurate and mature. Pure hubris. Every program I ever worked on had unanticipated show stoppers which surfaced during flight testing and required panic fixes, yet that basic lesson seemed to have to be constantly relearned.