The Wirecutter/Sweethome states that part of their review filter is that reviewed products must be available for purchase online. This results in the exclusion of a lot of specialty and other retail-only goods.

I will note that for many products, they have recommended items not sold on Amazon, even over competing products that are available for sale on Amazon.

And let's face it: when Amazon sells the majority of goods most people are likely to buy (and that you are likely to review), "affiliate bias" isn't really that big of an issue because it just means you're comparing one Amazon product against another. At that point, the primary bias would be from recommending the most expensive product available on Amazon, thus earning the highest commission. And Wirecutter/Sweethome definitely doesn't do that.