Are there any jurisdictions that actually have such laws?Yes. You can tell because the tag will read something like "SALE! $5 when you buy 2!" and then have smaller print reading "Individual price: $2.50."
Moreover any such laws are trivial to bypass by gluing multiple packs together (like they do at costco) and selling that as a separate sku.
But that's not what we're discussing here. We're discussing discounting existing items when bought in bulk, not creating new items.
To your point, though, creating a new SKU is not without its costs, both for the manufacturer and the retailer. If you're selling something in someone else's store (supermarkets are the example this thread is dealing with), you don't get to just make up SKUs and products on a whim. Think about the logistics involved.