Ask HN: Why do all shopping websites look the same?

I have been looking at various shopping websites, and to me they all look the same. Nordstrom, Amazon, Half.com, Etsy, Ebay. Category bar at the top. Hero Image and search bar. Some content below the fold.

Is this because this is the ideal way to shop for things online, or everyone just copies each other and converge on the same layout?

I realize at this point this category is pretty mature, but it just strikes me that there don't seem to be many "alternative" layouts for shopping websites.

Any counterexamples (or perhaps push back on my argument) are welcome.