Those indictments come from a group of people who hear only one side, there is no one there to question the validity of what they are told, and they are basically being asked to let it go to court and so I don't think they see it as so bad if they are wrong, it can work out in trial.
"Well if a grand jury wishes to bring charges, it must be a legitimate charge, or they'd not bring it to them."
It's akin to the idea that if someone has charges for a crime, that because they were charged they must have did it.
While that may be true, DAs don't like to lose in court, so why would they bring spurious charges? In this case, they would bring spurious charges because of the politics, but in general, they need a motive to take things to court that are obviously not even suspicious.