Now we have to understand why they apparently completely lost control. I remain perplexed.
Maybe English is not your first language - I don't know- by I find your use of the word "perplexed" extremely perplexing.
I would have thought anyone with even a rudimentary knowledge of aviation could easily come up with several obvious scenarios as to how the aircraft came to the fate it did - given the circumstances we already know. Some choose to speculate, on here and elsewhere, some choose not to. I choose not to, but I would observe that some of the comments on here regarding age/experience etc, show a degree of a lack of awareness of how dynamic and variable human factors are.
Maybe that contributes to your puzzlement, maybe it does not. Either way - no offence meant, and my condolences to everybody affected by this horrible tragedy.