What do you mean? There's plenty of motive for hijacking, just as always. Especially a flight filled with Chinese civilians headed to China. There has been a rash of terrorist attacks within China recently from Xinjiang separatists, including several different mass stabbing attacks just this year which have claimed dozens of lives.
One might hypothesize that terrorists managed to take control of the airplane and divert it only to have the passengers counter-attack and then in the chaos that followed either control of the plane was lost and not able to be recovered or it was intentionally crashed. Even with reinforced doors it would not take very long for highly motivated individuals to breach them, whether that's the attackers or the passengers or whomever.
I'm not saying that anything of the sort is likely but similar things have happened before.
One might hypothesize that terrorists managed to take control of the airplane and divert it only to have the passengers counter-attack and then in the chaos that followed either control of the plane was lost and not able to be recovered or it was intentionally crashed. Even with reinforced doors it would not take very long for highly motivated individuals to breach them, whether that's the attackers or the passengers or whomever.
I'm not saying that anything of the sort is likely but similar things have happened before.