"All the cases prosecuted involved some combination of: clearly intentional and willful mishandling of classified information; or vast quantities of materials exposed in such a way as to support an inference of intentional misconduct; or indications of disloyalty to the United States; or efforts to obstruct justice. We do not see those things here."
Interestingly, those who are strongly opposed to HRC use the term "traitor" frequently. It'll be interesting to see if the more fringe elements pick up on "indications of disloyalty to the US" as the reason why they think this should be prosecuted.