We like to think about whether we "deserve" what we get, or whether someone else deserves what he/she has. But in reality there is no such mechanism.

So you're saying we like thinking about a moral property, but we're wrong to do so, because this property is not reliably instanciated? Desert theorist do not need to disagree - there's no law of physics that means people necessarily get what they deserve. Rather, we are supposed to be the mechanism - we must regulate our own affairs so as to ensure that people get what they deserve.