I'm not based out of US, so the experience will vary. My understanding of drivers getting bad marked is that here the demand for Uber at peak times is still larger than the supply, hence even though you might be penalised via de-prioritisation, uber would still get you a ride to fulfil. They are also penalised by being given lower pay incentives. But talking to most drivers, the trade-offs of cancelling are worth it for them, since they often cancel drop locations from where demand would be lower, or to far off places where they wouldn't get another ride to complete, or have to go out of the way to return to the area they generally are comfortable operating in.

Whenever I've raised this issue with Uber(via their absurdly bad support feature), I generally get an automated response in the line of "We're so sorry for the bad experience, we understand that this has caused you a lot of trouble... We take your feedback seriously..", etc.