The BBC, like a lot of news orgs, wants to maximize advertising impressions, and the way to do that is to keep almost all links pointed to itself. A link to the more substantive source is a reader lost.
the BBC is to a large degree publicly funded and a public service broadcaster, and advertisements are only shown outside of the United Kingdom. IIRC over 75% of their funding comes from British license fees, most of the rest from licensing their content to third parties outside of the UK under a separate commercial branch.