I don't know that they _can_ move away from it, as people really enjoy clicking on the stars and actively "voting". It's cathartic, for the user. So, the usefulness is probably more about retaining user loyalty than merely gathering high-signal information.

A lot of the ratings are just garbage, like trolling mobs, bots, the competition, or idiots complaining about the package being dropped by the postman, or whatnot. They quietly drop or underweight all the garbage, and overweight their power users and real customers, to keep the overall rating relevant.