Why kill the bacteria? Because once they get their little village created they will not be overcome no matter how balanced you make your biological terrain. Doing that is preventative, not curative.
That is only an assumption that bacteria will return and reinfect. I once used electricity to kill an infection inside a tooth (verified by my dentist) and the infection never came back.
The problem is the no-good dentists charge too darn much and using electricity to cure the problem is way way cheaper than spending thousands on those greedy thieves.