At first I thought you meant it can't be rotated, but no it can be rotated, it just can't be flipped over.

If there's any kind of bevel to the blade or other non-symmetry, this makes sense. I mean, the carbide inserts on my jointer don't work when upside down.

All this said, I've used the same no-name brand of windshield scraper my entire life and I've never worn one out.