I like the hovercards, but why do the preview pictures only show up in some of the link's previews? For example, there is a picture on the hovercard for a link to the McLaren 720S article, but not for the article about Buick. I would like to see the picture every time , so I can have a better idea of the subject. (except for those few articles that don't have pictures, of course)
Topic on Talk:Page Previews/Flow
Howdy. Great question. This is due to a decision to not pull images from further down the page than the lead section. It ended up that many images used that were not in the infobox or introduction were confusing to see paired with the subject matter.
For instance on the Buick article, the image regarding "Valve-In-Head engine" would have been the image used for Page Previews prior to this change (the Buick logo is a non-free image). While related to the subject, as the article is structured today it wouldn't have been nearly intuitive as say a photo of an actual Buick. :)
A little more technical information can be found here: https://phabricator.wikimedia.org/T87336
Non-free images were a problem for the Related Pages feature. Later I opened a community discussion which accepted non-free images in Page Previews. That resulted in T131105 for Page Images to support any-image or free-only, and T147317 to enable non-free images in Page Previews. Both are marked as Resolved.
Something is wrong if Page Previews isn't showing non-free images.
I'm not certain, but I think I recall something about avoiding images with an extreme aspect ratio. Maybe this image is being skipped because it is very short & wide?
@Alsee's assessment is probably correct. The aspect ratio of the logo (the only image above the fold), is not of a dimension that makes it eligible to represent the the page.
Ah! You're both right. I misunderstood the question.