Both Farley and rvblyky7 are onto the explanation, IMHO
The swept wing jets have much different stall characteristics than the straight wing jets.
Take a straight wing up close to the "critical mach" and note aileron reversal, some buffet usually from the ailerons, loss of pitch control, etc. Then pull on the control stick/wheel. Whammo! May not resemble a "conventional" stall you get when low and slow, but an outright "departure". Think rapid roll, yaw excursions, pitch excursions, etc. i.e. a departure.
The swept wing planes have a more "gentle" entry into the departure unless you really command a large pitch/roll change when close to the critical mach. Some simply settle into a sustained aerodynamic stall such as we saw with AF447, with minor roll oscillations and such. That one was more of the basic aero stall, but there were some mach considerations at play early in the game until the jet had zoomed at a decent angle and lost EAS AND mach.
Good discussion.