That approach may work for journalism and such, with a single person collecting primary sources and verifying them before writing an article. However, it does not work on the internet.

Instead of one person verifying the claim and adding further sources in an article, every single reader would have to do it. And anyone using the internet would have to do so hundreds of times every day. Nobody does that. It only makes sense to shift the burden of further proof onto the primary source or disregard it.