Articles are often made intentionally too long (ever notice recipes that force you to scroll through loads of irrelevant copy about the ingredients before you can get to the ingredients list and directions at the bottom?), this probably has to do with advertisements which will fire off when you scroll far enough down the page, it counts like an additional page view and the site makes more money.
Yeah, though supposedly SEO could actually penalize articles for something like this, the SEO requirements keep changing but I bet there is a balancing act between keeping SEO happy and keeping up your ad impressions.