The proof is reportedly of the standard which can be admitted in criminal court proceedings, so certainly they will meet civil standards.
The Supreme Court has ruled government agents can be personally sued for violating civil rights.
Voting rights are civil rights.
So people should start filing lawsuits against these corrupt county officials in Maricopa and Fulton county. At the very least it would give them fear to do it again.
Start now before the next election gets here.
You question is a negative: Why can't they sue them?
Difficult to say, and depends on your jurisdiction, although in many jurisdictions the STATE has been and remains to be sued.
individual perpetrators however ......
Often are hidden behind a veil. In some jurisdictions the prosecutor or adjunct prosecutor will make a determination based on the facts of the case, resources, consequences. The STATE prosecuting his own? Like a butcher inspecting his own meat?
There may be a process allowed to sue the prosecutor and force him to prosecute.
And then comes the appeals process. I have seen a slew of suits being struck down by all kinds of judges, until one judge said: no you're right. The time for appreciation is over, rights violations cannot b tolerated, only to be struck down by a superior court within 4 hours the same day, wheras an appeal takes 4 - 12 weeks of prep!
You would have to do it, even just for the sake of having done it, and the process itself is proven larded with activist PRO bi government judges.
My question is rhetorical.