Dang, I just realized I didn't post any fixes.
First, confirm there is EXIF metadata in the original image file. Use Preview.app or maybe QuickTime Player. If the app shows the metadata, then the next step is to trick Spotlight (technically, its mdworker process) into extracting the EXIF metadata into the Spotlight system-wide metadata store.
Second is how to trick Spotlight into reindexing. Here's several possibilities, roughly in order of complexity or time.
Simply moving the original image file into a folder may trigger Spotlight. Try this by making a new folder, moving one original image there, then check what shows up under its "Get Info". If it shows the extended info, then move the file back to its original folder. Repeat for as many image files as desired.
It might work to tell Spotlight to disable indexing, then re-enable it. To do that, drag the Documents folder (or the subfolder with images) into the Spotlight : Privacy sub-pane of System Preferences. This will effectively remove all metadata from the folder contents, and prevent Spotlight from indexing it. Then you delete that folder from Spotlight : Privacy, which re-enables Spotlight indexing. Give it a few minutes, then check with "Get Info" whether the EXIF metadata has been extracted.
If simply moving an original image file or Spotlight Privacy doesn't trigger Spotlight, maybe compressing and decompressing the files will. See here:
https://support.apple.com/kb/PH25411?locale=en_US
Basically, you compress the originals, move the originals to the Trash (don't empty Trash yet), then decompress the ZIP file. At that point you should have all the files and folders you started with, in their original location. Use "Get Info" on the newly decompressed files to check for the extended info. Whether this works or not, you can empty Trash now, because the decompressed files should be identical to the originals. Best case they show extended info in "Get Info", and worst case they don't. Either way, the files themselves should be identical.
Also, remember that copying from one folder to another caused the "More info" to show up (the Desktop is a folder), so you can try that using a new folder rather than dragging directly to the Desktop.
If compress/decompress doesn't work, and you have an external USB stick or drive, copy to that, delete originals, then copy back.
If you don't have a USB stick or drive, you can create a disk image file using Disk Utility, copy files to it, delete originals, then copy back.
I can probably come up with more things to try, but they involve command-lines in Terminal, so try all the above first. If none work, ask again.