[Saintly]

The official reason was that they where running extremely low ground clearance to produce large amounts of down force (you remember all the sparks that F1 cars used to make out the back). They went a little too low and he bottomed out for a split second in the bumpy corner. That stopped all of the down force provided by the body and he lost traction and speared off the track.
The car telemetry showed he was making steering adjustments up to the point of impact so the steering was not broken