From their own data, Inmarsat can't say whether it was going North or South: they inferred that North was unlikely, as someone would have seen it go by.
The north path would be very embarrassing for many people.
The south path hypothesis (fire - decompression - zombie a/c), however unlikely, is the only one that allows to save face for all countries (eastern and western) affected in some way by this 'event'. Any other explanation would point to incompetence or worse, misbehaviour by some governments.
So I guess we'll have to buy that one.