Which is why some shops re-use them. I think the law may exist because not every tire tech is competent or going to do it with care. I can see where over tweaking a piece of spring steel could weaken it or hitting it could weaken the bond of the lead to the clip. But you know how it is, if even a small percentage do something badly and someone gets hurt some politician has to do something about the "problem" so a law gets passed.
We had one state legislator try to ban certain breeds of dogs from the state because of a dog attack in his district. Imagine someone or a few people got hurt or had near misses from flying WW's and there you go. Or the lead manufactures lobbied for it and no one was paying attention. Be a good deal for them, when they are removed from the car the old ones get recycled into the new ones getting installed.