The reason reviews are among the elements considered for retail readiness is that reviews help to build credibility and trust for a product.
You can check Amazon’s training course for optimizing for retail readiness. In fact, Amazon has a lot of resources like this to help you understand how to be successful in selling on its platform.
https://advertising.amazon.com/library/courses/optimize-for-retail-readiness
Why does Amazon offer these free courses? I believe it’s because their financial success depends on their seller’s success with using their platform. If we make money, they make money… and everybody wins, right?
In my experience, of all the elements that make a book retail-ready, getting reviews is the hardest part. Let’s face it, most readers just don’t leave reviews. It’s not always because they don’t like the book. People have busy lives and sometimes forget to leave a review or rating. Others may not feel comfortable writing a review. The list could go on and on. And sitting around waiting for reviews to come in organically can be an exercise in frustration. Yet these reviews are critical. So, what is one to do? Well, the answer is not as hard as you think. You have to actively ask readers for reviews.
The key is being creative in your approach. Whether you offer something like a free review copy in exchange for an honest review or use services like NetGalley to find folks to help you out, the ability to get those reviews is possible. It’s just going to take time, so don’t give up!