This is so very typical of "old-school" news organizations that do not "get" the internet, nor do they understand the power of connections (HTML links in this case). Of course, the lack of "getting it" is somewhat understandable given that these old-school orgs. are coming in to this "new-fangled" internet tech. with a mindset grounded in 100 years worth of creating paper for dissemination of information. Since paper ca not directly connect a reader to a base source, they never saw any reason to provide the information necessary for a reader to obtain the base sources for themselves. And they continue this practice onto the web, which from their mindset is just another "paper printing press" to disseminate information across.
Additionally, there's the somewhat conspiracy theorist viewpoint that hiding the base source information is overtly purposeful on their part, because that way they can have a better effect in influencing opinion (because the only data you get is that which they deem you suitable to receive) and without any ability to get to the base sources, you are much less likely to form any independent opinions that might diverge from what they want you to believe.