To my knowledge and I am prefacing this with I could be wrong. In order to charge Hillary for the email incident they would have had to prove either Intent or Gross negligence and when it came down to Hillary I dont think the Doj had anything along the lines of these two factors, whereas trump and they even qoute him, hes talking about how the information is still classified but yada yada this happened, that fills the intent part and then for the gross negligence part they talk about how they found the boxes of files just strewn about everywhere in the club.

Feel free to correct me, this is just my understanding.