People are talking about an uncontrolled pitch down manoeuvre or ’bunt’ to bring about the final dramatic loss of altitude.
Another scenario could be that, during the attempted turn to return to the departure airfield, the aircraft suffered some sort of uncontrolled rolling and pitching manoeuvre. This would be especially likely if the ‘assistance’ of the MCAS was disabled via the Stab Trim in CUTOUT and the aerodynamic moments at high alpha, that the designers predicted, were in play during a ‘steep’ turn. An increase in the pitch up moment due to a simultaneous increase in power may also have contributed.
A real AoA increase during a hasty hand-flown turn regardless of any incorrectly sensed, and now managed, systems failures may have resulted in a loss of control.
The aircraft designers seemed to have anticipated that this aircraft would vulnerable to pitch excursions at high alpha and installed the MCAS to assist in this case. With it disabled, and flight crew muscle memory anticipating different performance from a legacy 737, they may have inadvertently and tragically placed the aircraft in a non-recoverable unusual attitude.
(I’m not a 737 driver although I have experience in a similar weight category and a reasonable knowledge of aerodynamics. I have read the whole thread.)