"On July 3, Marks' organization and state voters filed their lawsuit, and on July 7, technicians at KSU wiped the server. When the case later moved to federal court in August, technicians wiped at least one additional server one day after a federal judge was assigned to the case."
https://fcw.com/articles/2017/12/08/wray-fbi-georgia-electio...
It doesn't matter if there is some law requiring you to destroy that evidence, because there are also laws requiring that you not destroy evidence of crimes.
Just assume that the people involved in the voting process don't understand data management and storage practices or things like access control or asset value and have no budget to train or retain, and it makes sense. The upload interface was depracated, unpatched Drupal of that's any indication of their IT effort. Set it and forget it.
From what I was told, the FBI already had copies of the data, and I'm sure a college who gave the state some space and services to run things didn't want to be responsible any more than a datacenter would want to be for hoating a MEGA storage node after the Dotcom raid. Get the hot potato out of there, let the law enforcement handle it.
This means no data was lost or rendered unavailable, just that it would be the FBI's responsibility to furnish that evidence in event of any further lawsuits.