By choosing images over links, and by restricting markup, Facebook, Twitter and Google+ are hostile to HTML. This is leading to the plague of infographics crowding out text, and of video used to convey minimal information.
The rise of so-called infographics has been out of control this year, though the term was unknown a couple of years ago. I attribute this to the favourable presentation that image links get within Facebook, followed by Twitter and Google plus, and of course though other referral sites like Reddit. By showing a preview of the image, the item is given extra weight over a textual link; indeed even for a url link, Facebook and G+ will show an image preview by default.