I believe its pretty much like this Ts, when you takes something out of equilibrium this something wants to come back to equilibrium. However when you reach too far from equilibrium, and the thing try to equilibrate itself it just cant because it has more energy than could handle in equilibrium... so it got to become something else.
Think of a piano... If you add 1meter of gravitational potential than let the piano fall in the ground it will get damaged...
If you take this piano 10meter higher than when you let it fall it will get completely destroyed...
When the high voltage pulse frequency is applied to the water the water ions get ionized this mean free electrons and positive ions, If you than make them to combine there inside they will do so with the simplest configuration possible, assuming recombination to water will be only a small portion...because electrons have a ratio of charge to mass much greater than the H+ ions and far much greater than OH+ ions, this mean the speed of the electron in comparison must be several magnitudes greater.... They should want to go to the lower energy state but this is far apart at the other side of the cell than the simplest configuration in terms of molecular scale. Stan stated that its only related to the deflection and movement of electrons...
The ion and electron feel the same force but as the masses are different if strong enough force is applied the electrons are accelerated much more than the ion... and when they split (ionize) they will go in opposite directions despite the fact they still attract each other.