You wrote: " Also, diesel engines are more complicated than petrol engines and thus require more energy and materials to manufacture." which isn't exactly true. Okay, it's wrong. Diesel engines are essentially a block of iron. Unlike gasoline engines ( and stop calling them petrol. This is an American Bsed website) diesels don't need high tension coils, distributors, spark plug wires or even spark plugs. One of heir charms (and they need them, because they have their downsides) is the comparative simplicity.

Really it's a wash. While Diesel engines don't require an electronic ignition system, they require a precision, high-pressure fuel injection system (and by high pressure we're talking on the high side of 20,000 psi), careful design of the combustion chambers, pistons, etc. to get efficient ignition and clean combustion, and detailed attention paid to materials and casting/machining to deal with tight tolerances and high temperatures in operation.

The hidden advantage of this is longevity. A well-maintained diesel engine can run a million miles without significant repair. The barrier to entry in the price-oriented US market is that the engine itself, with its better materials and engineering, costs a bit more and Americans tend to take the short-sighted approach. They're only going to keep the car a couple of years, after all, then trade it off for something new and shiny and end up owing more than their car is worth, so why bother to buy something efficient if it costs a bit more and will take 4 or 6 years to pay off the extra cost? They'll only have it 2 or 3 years.