Why does Trump display more animosity towards CNN than he does towards ISIS, Kim Jong-un, Bashar al-Assad and/or Vladimir Putin?

Because he is a fascist and all the little trumpster fascists are falling for it.

He's trying to shut down criticism right now.
After he gets CNN, he'll go after the newspapers.

He already has the Washington post and the NYT in his sights.
Fascists always go after the free press. It's what they do.
Trump would like to keep the National Enquirer and Fox going, and outlaw all competition. That way, he'd have a de facto state press.