for sprinkling in the foundations of a new structure maybe, etc.....would they just be discarded there, like so much useless ....errrr.....stone chippings?.....
Just a thought
If I'm a guy who wants to make and sell "healing amulets" there's no reason that I need to believe in the healing power of the stones, just so long as I know there's a market of willing believers out there who are going to buy my goods.
So I wander up to stonehenge and chip off ten "amulet sized" chips for fashioning. In the process I cause a shower of smaller fragments to fall into the grass at my feet. I'm not going to necessarily get down on my hands and knees and collect every last one if they don't have any value to me as an amulet maker and seller.
As I've said earlier, there's no way to confirm this theory so it's all just speculation and I'm certainly not saying "it's definitely right". But it's not that difficult to construct a plausible scenario such as the one I've just mentioned.
And you can construct other equally plausible ones no doubt to support other theories. But there's nothing fantastical about the 'healing amulet' idea.