Well I reckon it's more to do with what they are used for. Until recently, diesels were most often found running trucks, tractors, generators, locomotives or boats. They would usually run around the maximum torque point, run for days or months without stopping, maintain constant revs and temperature, and not get thrashed. Petrol engines often had a very different life with frequent stops and starts, cooling down at night, and revving hard right through the range when in use. Perhaps if they were operated in the same way as a diesel they might last almost as long.But I know next to nothing about engines.
