The only explanation: Hydroplane

Hydroplaning occurs when the tires' tread is unable to expel enough water to maintain a rubber contact patch on the road. The function of tread is to allow the "high" part of the tread pattern to cut through by forcing water (and other road grit) into channels and grooves surrounding the tread blocks. When the water gets too deep for the tread grooves to cut through it and force it between the tread blocks, the "high part" of the tread blocks lose contact with the pavement and looses traction by hydroplaning