Question: What can I do to develop my muscle for generating themes, purposes, and content, as very often I haven't used it, focusing mostly on style?

Answer: 
Copyright attaches to a work by the act of publication, or sharing the work for the purpose of publication.

A newspapers/websites own their original stories. Those stories that they publish gain copyright protection.

If an organization reproduces other source articles verbatim and without permission, then they are at risk for legal action. That legal action is costly to pursue therefore it isn't often sought by newspapers/websites who believe their copyrights have been trespassed. That fact doesn't prevent everyone from doing this as it is a common practice for some web sites.

If the original story is quoted or summarized, and not reproduced verbatim, then it would be generally covered under "Fair Use" doctrine. But, fair use, was with copyright law, is not a precisely defining property. Many court cases have been unexpectedly won or loss based on the court's interpretation of the exact details of the case pertaining to fair use.

The definition of Fair Use and the letter of the law are one thing. The only true determinant are the decisions of courts in copyright cases. And courts are all over the map, making black and white declarations of what is and what isn't a violation a difficult subject in certain cases.
I'm not a lawyer, but my understanding is copyright is about intellectual property. I created the idea, therefore I own it.

If a news outlet re-writes a story, they weren't there. They don't own the intellectual property. Somebody else does.

Why should I benefit from somebody else's work? If I re-write a novel using the same characters and story, I am stealing another person's ideas.