(non pilot speaking) I understand that one of the causes of this kind of event is air currents swirling around airport buildings. For example, at LHR, the maintenance hangers at the eastern end, can produce a strong current across the runway at the critical moment.
Also, the head wind can vanish suddenly and other unexpected changes in wind. If the machine is only four or five feet above the ground with a steady sink rate - when this kind of wind change occurs - there is nothing that can be done and the shock absorbers will earn their keep.