I checked the age of the plane and it's only 9 years old, which is relatively good for a 777. What would cause a 9 year old, 300 million dollar aircraft, to be suddenly leaking oil.. having fuel issues that can cause a fire such as this on landing?
Major maintenance snafu, undetected oil/fuel system component fatigue, or turbine disk/blade/burner can failure are some of the typical man-made causes.
Why the fire bottles failed to confine the fire to the nacelle is a big question - if they were discharged in time and there was no disk/blade failure, which seems unlikely as that event would have gotten everyone's attention pretty quickly.