If it were merely the executives that made the fatal decisions regarding the 737 MAX then clearing out the top level of management may suffice, but it's fairly clear that it wasn't a C-level decision in this case.

Once you have a bad culture established in an organization it's very hard to turn that around absent a rather drastic purging of employees at multiple levels combined with a very pro-active new management that not only talks about the necessary new culture but also actively implements the incentives required to enforce such a culture.

Personally I've had to deal with cultural turn around efforts at companies in the past (albeit nowhere near the scale of Boeing) and over time I learned that the only reliable way to address such a situation is to purge with fire and bring in new people.