Amazon calculates a product’s star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers, and factors that establish reviewer trustworthiness.
I must have not read the description very well - I thought is was 1 card for any one of these 4 restaurants. I felt like I was being cheap for getting 4$15 gift certificates rather than 1 for $60. I know it's the same, but to me, it's not what I expected.