The work was first posted to arxiv in 2012. It can take a while until a result is understood by enough experts to confirm its correctness. Imagine if journalists wrote an article claiming P=NP is closed every time someone posted their attempt to arxiv.

Also, this work very recently won a prestigious award.

Also, result published ---> result accepted ---> journalist writes high-quality piece explaining result to lay people can take years.

> the lack of an actual citation was very disturbing

The first linked text in the article is a link to the arxiv paper.