By default, journalists don't link to their sources----not if its a scientific journal, another newspaper, a blog, a tweet, or anything else. They do tell you

By default, journalists don't link to their sources----not if its a scientific journal, another newspaper, a blog, a tweet, or anything else. They do tell you the source, but leave it as an exercise to the reader to find where it is. So this isn't bad etiquette so far as the group they're conforming to is that of other journalists.