They went from being the bottom of the league without any assets/draft pick in sight to becoming a playoff team. They built a foundation and Atkinson was at the helm. He was very successful, held his players accountable, good personality, and committed to turning around the franchise + being liked by everyone in FO.
He liked guys that played hard, and the guys played hard for him. Last year’s Nets were an absolute joy to watch. I’m stumped as to why exactly he’s gone all of a sudden, but I guess considering KD/Kyrie's temperament, they probably didn't like him as much. People complained about him giving up the most blown double leads in the NBA, but... I think that is more on personnel than anything.
He'll be picked up by a team soon. Knicks/Bulls would be wise to hop on this chance. If Fizdale can get multiple opportunities, so will Atkinson.
EDIT: Actually pretty dumb considering KD said Atkinson was a huge reason for his arrival.