Small images don’t show metadata on hover because they do not lightbox, that is, the entire image fits in the post.
The behavior feels slightly inconsistent at least, since multiple images on the same post offer metadata on hovering or not depending on whether they are small or large, but for the reader at this point there’s no distinction between such images because they’re all the same size. The behavior feels arbitrary.
I’d suggest showing at least the details on hovering, irrespective of the image size. Then perhaps not expanding for those which are small.