Muilenberg became CEO in 2015. The McDouglas thing happened in '97. He inherited an existing management structure that was already primarily interested in profit over all other concerns, especially engineering.
Moreover, the 737 Max program ran from 2011-2015. The CEO at the time was an MBA.
As an engineer, he was accountable to reality. As a CEO, he was accountable to the board and the financials.
Guess which won.