the other theory is they targeted Clinton because they thought she'd win and were going to use what they stole against her.
http://www.nytimes.com/2016/12/13/us/politics/russia-hack-election-dnc.html?_r=0
chances are they were working every angle they could and left unchecked became more and more brazen.
I could see that. It's not like either had a shortage of their own scandals but I could see how specifically attacking Hillary could help destabilize the nation's confidence in its elections as opposed to Trump whose scandals have a tendency to slide ride down his greasy back.