Sometimes the provider might design their star rating system purely as a consumption experience, not as a recommendation signal. Not every product has the data or reasons to use star ratings as recommendation inputs, and I'd expect that most people look at star ratings next to an item and use that as a quick gauge of whether it's good or not.
Assuming the amount of traffic (drive-by glances) is considerable, compared to the number of times you personally get recommended something. Should users submit star ratings for their own purposes, rather than the greater good? I think there are several arguments for "no", but the murkiness is the real catch. If people think their stars are being used for Netflix-style "We think you would rate this 4 stars", but the only actual use of them is to show other people how the product ranks on an arbitrary scale, then both sides lose.