Some humans like to participate in things for the fun of participating in things. They may not have even bought the product. They just give a 3 star rating because they don't know. Some other humans like to form beliefs about things before buying them, and they'll give it a 5 star rating beforehand. Some people, like the kids you find on this website, like giving everything 1 star ratings 'cause they love emitting negativity in everything they do. People have different tastes, so even if they have copies of the same product, they'll like it for different reasons, and they may even use it for different reasons.
So, what's the point of building a wonderfully accurate mathematical model for sorting this data, when the results that you are processing are mostly garbage?