That's basically an exploit. Different 'products' can be related, and the reviews are supposed to be useful across them. The most obvious examples are just different colors of socks, or different sizes of shirt. Sometimes it's variants on a product: one with a handle and one without, or different models of TV with the same screen, or whatever.

But it's not Amazon who makes those connections, it's the companies entering product data. Some of them abuse it, and say products are related when they're not at all. Since there's millions of products listed, it takes time to identify and fix the false associations. In the meantime: people looking for headphone stands see reviews for whisks.

But yeah, quality has gone down. It hits some product categories a lot worse than others: cheap electronics is a shitshow.