The computer mouse allows to easily scroll vertically, so why are most of the standalone image viewers (lightboxes, etc..) not taking full advantage of the vertical scrolling to browse images?
The sense is to concentrate visitor's attention on one picture, not many, due to rather visually noisy nature of photos and to increase percepted value of every certain image, not the whole collection.
Also using scroll it is hard to achieve good aligment – it is not esthetically pleasing to see part of one image at top and another at the bottom (even with some noticable margins) and requires additional efforts to scroll the wheel individually for every image with different hights.
So it is possible to put images in the column, but there is usually no need.
A lot of social content sites like BuzzFeed actually do prefer to plop all their images together vertically (here's an example). I've noticed news sites tend to favor a previous/next paradigm instead (like this).
If I were to guess at the reason, I'd say that in the former case (vertical scrolling) the images/videos are the content, so you need to allow rapid, easy browsing (just like you wouldn't make someone read a text article one paragraph at a time; you put all or most of the paragraphs on a single page). In the latter case (previous/next paradigm), the meat of the content is the text, so you make sure that dominates the page and the images use up less room by being lumped into one place.
I can think of examples that don't follow this logic, though, like this Boston.com article that shows its main content (great dates with images) one at a time. The two reasons I can imagine for this are: