Because it's actually 99% content? It's a slightly jarring look when you're used to "I know you're trying to read this, but here's 10 more articles that look better on our engagement rates than simply scrolling".
It's a major newspaper in Spain. First or second in the country depending on whether you're counting by online or print readership. It doesn't exist just for one article.
(Although with a little clicking around, it does appear most articles have a sidebar, and this one doesn't. No idea there.)