Re: Why another case in the USA ?
It's worth noting that while US prosecutors work for the state (Federal or one of the several States) and officially represent "the people", it's the choice of the prosecutor and his or her office, not "the US" or "the courts", to pursue the criminal trial. I suspect the overwhelming majority of government officials in the US, at all levels, don't give two shits about Lynch, Autonomy, and HP(E).
The various prosecutorial offices in the US have become highly politicized over the past few decades,1 and prosecutions big enough to make the media are generally driven by the ambitions of prosecutors more than anything else. Favors to the wealthy (e.g. HP's board members) also play a role.
1See The Chickenshit Club and some of Ken White's posts on Popehat for details and supporting arguments. White used to be a Federal prosecutor.