People like diversified answers. People look at webpages at as a single entity so even if there are a million reviews on one site they still want a 2nd opinion from another site to reassure them. or a 3rd or fourth site and this is where you can capitalize.
Lets say they went to Amazon, then the searched out a product on a taco maker and then decided to review it off site and found your site "tacomakersreviewsite.com" they read about it but on your site you have an affiliate link hooked up that exact amazon product. 99% of the time they will use your affiliate link to redirect them back to the product and buy it. THUS CREATING INCOME!!
FYI to answer your question. Competition is based off people buying ADS so they will put more money into the specifics of their product over the vague searches as it drive targeted traffic.