He posts the story so his 1-2 hour video (which is his original content from his daily show) has a context for his followers. He isn't presenting the stories he is sharing as his own, and usually he is dissecting/disagreeing with the slant of the article he is dissecting. Maybe try watching one of his videos that is on every single post.

If you watch his show, you will see he references the article in question. He also often will link to the article, but not always as his referencing (often ridiculing) the story in his actual video keeps it from being plagiarized content. The fact is many of the articles he is sharing, he would NOT want his audience thinking they were his thoughts. Hence, the videos he makes to clarify HIS thoughts on the matter.

Given his net worth (and capacity to earn from his loyal follower base) if he was stealing others content and passing it off as his own, he would be sued successfully by many people (given he does several shows a day) and not be worth millions.