IF the info is THAT damaging, why would it still exist? Why not just destroy it.
Holding that information over the heads of the DNC gives extraordinary power to the FBI.
I think they know that others with access may have downloaded it to thumbdrives as well, for "leverage", and they can't take a chance on denying it, only to have, for instance, a revolution inside the FBI from the patriots remaining who have had enough. Since then, they have made a concerted effort to dump patriots from their ranks.
And above that, the NSA servers probably have a copy—and who knows who could have purloined the contents over there? No one thought that former NSA chief Admiral Rogers would straightforwardly and within the law contact Trump and warn him that he was being bugged at Trump Tower during the 2015 campaign, but God bless Rogers, he did; and it set all this unraveling in motion.
Slowwwww motion.