It's an XF2 performance optimization. Some things need to be taken into account when undoing it such as not displaying GD images outside of GD.This comment looks this way, on mobile. Clicking the link takes you to a new tab just with the image displayed. Ideally, it just displays correctly in the quote like a normal hotlinked image.
Generally the problem with images and quotes is that people don't trim them, not the opposite. So this would probably make the forum experience worse 75% of the time when viewing quotes of attached images.