Because if your doing 1000+ miles in a week I would want something that does 50mpg or close to it. The diesel engines arent made to replicate the petrol engine, I'd maybe say the opposite. Diesels have powerful (torquey) engines because of turbo's and other clever designs. They are made to make effortless progress as the low rpm's is where the power is. The makes town driving and over taking easy and negates have to constantly change gear. But arguably less fun on the b road but I can still get my kicks.