The charitable view is that this saves bandwidth (and load time) for page views that never get scrolled. Also, it may allow them to count the ads in those sections as impressions without having to paginate the article, which presumably they know that people hate.

But I think it's ironic for an article about open access to make itself essentially unprintable in this way. It's too long for me to read on the screen. A "page of HTML" would be demonstrably superior for that purpose.