It's early to speculate on reasons, but some witnesses say they've heard a poping sound, like in a compressor surge. There could be many reasons for it (bird strike?), but if he was in a forced turn at low altitude, when both engines are on AB, failure of the lower engine would create a huge assymetry and thrust difference pointing the nose down, and there is nothing that could be done.
No airplane would save him. Stricter rules could have. I hope we will learn form our mistakes, while we did not learn from others'.