Re: this whole thing could have been avoided
Well part of it too is that if you prosecuted Hillary, democrats would be calling for an investigation of former secretary of states Powell and Rice, neither of whom used official state department email but used their own for all their official business. It is unlikely they operated any differently than Hillary did, which is probably why career (i.e. not partisan appointees) state department officials never flagged Hillary's use of private email as a problem. They'd seen it all before, and to stick around a long time through administrations of both parties they know you can't be a boat rocker.
Biting the hand that feeds IT
