Probably terrorists took control and were planning to crash it into a target, probably in India or maybe Diego Garcia.
Either passengers did a Let's Roll or the terrorists couldn't manage to fly low without crashing.
Governments will blame it on a spontaneous explosion in a previously-unknown fuel tank located in the aft toilet.
Okay, I'll bite....why Diego?
In yet another oddity the cast for that was on MH370: Jet Li's stuntman is/was one of the passengers.