Actually, it does. At high zoom, you are just magnifying the JPEG artifacts and averaging errors. Such a magnified image is actually harder for the human eye to read. It confuses the human visual system, keeping it from seeing the forest for the trees, so to speak.
To see what I mean, look at this. Then step back across the room from your monitor and look again.
If you zoom into a small image of a face, expecting to count the zits, you not only can't see the zits, the face itself becomes harder to recognize. Same goes for text.
The above image by the way illustrates the effect of magnifying averaging errors. It contains no JPEG artifacts. They just compound the problem.