Why do some Pinot wines turn out great while others are a disaster?

I don't know much about grapes but it's likely to come from the chemistry of the grape, whether that's influenced by the soil or the genetics of the grape. The taste of wine comes from things called secondary metabolites that the plants produce and use to protect themselves against predators and attract animals to eat their fruit. So it's likely that different lines have different chemicals and that gives you different flavours in the wine.