If it is, it's not difficult to introduce a system to deal with it (and they may already have such a system). All it'd need to do is normalize ratings or at least reduce the weight of negative ratings if the rater always gives negative ratings.
You don't express derivation in the positive direction because delivering a product or service as described without issue is the highest aspiration. It feels wrong to make anyone dance for their supper.
Oh, and btw: it's the same the other way round. I also sometimes put much more effort than strictly required into my job for a particular client, and I love it when that is recognized and honored. If it is, I am more inclined to do it again later. If not...well, not so much, then it's probably back to "standard service, just enough to fulfill the contract".
It's very disturbing to me that the highest aspiration is to just "meet expectations". That seems like motivating everything toward mediocrity.
My highest aspiration is to exceed expectations.
Like why even set expectations in the first place if your bar for perfect is "impress me"? Why is "I did everything you asked" less than perfect?
Many apps, including Uber, now also give the option to commend the driver for things they did well (e.g. cool vehicle, smooth driving, great conversation), which is also an option to express specific positive feedback.