A bit surprised this hasn't been posted previously - it's from the Monday Seattle Times:
https://www.seattletimes.com/busines...ion-air-crash/
A former Boeing executive, speaking on condition of anonymity because discussion of accident investigations is supposed to be closely held, said that Boeing engineers didn’t introduce the change to the flight-control system arbitrarily.
He said it was done primarily because the much bigger engines on the MAX changed the aerodynamics of the jet and shifted the conditions under which a stall could happen. That required further stall protection be implemented to certify the jet as safe.
Side note - I'm a bit surprised even a 'former' Boeing exec was willing to talk about this to the press - this sort of information release during an active investigation could get them in some serious hot water...