Agreed it could be a bit quicker or more intuitive, but this seems to be a use-case I don't need to work with too often, so it's not bothered me.

I'm guessing there's a mix of performance concern and privacy concern. They want to make sure you're intentionally revealing the secret (image) and they want to hold off on decrypting the file until needed. It feels like decrypting a file is a fairly slow operation (although I'm not really sure why).

I just don't think comparing to the file in your local files is quite the same, since it's not encrypted / behind password protection. If you did this sort of thing a lot, you'd probably have it optimized down to a very accessible shortcut, after all.