The page accompanies a blog post about how many images have alt text on Bluesky so empty lines are included to give a feel for how many images do or don't have the descriptions: https://digitalseams.com/blog/image-descriptions-on-bluesky

> This demo is part of Image descriptions on Bluesky: not bad, could be better - see the blog post for more details!

Surprised then that so many posts are just images.