Why? A car with an engine about this size is more than adequate for long runs/high mileages and if all cars were restricted to engines of this size many environmental problems would be solved.
because when you are regularly travelling longer distances and higher milages a year it is more comfortable and practical to have a slightly larger car
mini = town car
supermini = extra urban
small family = above plus motorways
large family/exec = mainly motorways
also small diesels dont make sense when you include the extra purchase cost
http://www.parkers.co.uk/cars/petrol-vs-diesel/?deriv=46366#manu=2193&model=1662&deriv=46366