The more likely explanation is that people got tired of Assange's story and so the articles didn't get the clicks to justify covering them any more. The Guardian can get more clicks with a steady drip of vegan opinion pieces, stories laughing at Tories and the dreadfulness of brexit so that's what they'll do.

Same as the Telegraph will feed its readers "the glory of Boris", "forwards unto brexit" and "Good lord look what Corbyn said today, he's a dreadful little man isn't he?"

News organisations are slaves to their audiences and will just produce what their audiences want.