History tells us that it is likely to be a combination of smaller problems that lead to the crash?
From the scraps of information known he got low on the approach. Why and how he got there, and maybe why he could not correct the situation is anyone's guess at this stage.
Straightforward pilot error, distraction, mis-interpretation of the displaced threshold, carb ice, mis-management of fuel, problems when selecting flaps, some sort of pilot incapacitation, engine issues etc etc the list is long.