Why Are No Reviews Being Left for Free Products Under the Vine Program?

I’ve enrolled in the Vine program and provided free products to reviewers, but some of these products are not receiving any reviews. According to Amazon’s terms and conditions, customers are not required to leave reviews. Specifically, the terms state that Amazon Vine makes no assurances about the number of products that Vine Voices will choose to review or the nature of the reviews they may submit. However, if the products are being claimed, why aren’t we receiving any feedback? This seems unfair, especially when we’re giving away free products with the expectation of getting valuable reviews. What’s the real benefit of the Vine program if no reviews are left?