Brad Raffensperger won Cobb and only lost Gwinnett very narrowly on a night when he won statewide by 4, even after Abrams had carried those counties handily in November and the D base in the state was still energized. With a better D performance in the Atlanta metro, Democrats could have easily won both runoffs.
In retrospect, losing Cobb was about as surprising as Gillespie winning Loudoun in 2014.
I guess in part the Raffensperger was from N. Fulton vs a rural D, plus as mentioned weak turnout for an SoS race.