Why do marine engines weigh so much for that power? An airplane uses ~100MW (depending on how you want to calculate it) but obviously its engines don't have a combined weight of 200 tonne.
Ship engines are the way round: their weight doesn't matter much, but it matters that they use the cheapest fuel possible.
Small correction: aircraft engines generally use kerosene-based fuels (Jet A-1, Jet B). Also cost-wise, aircraft-grade kerosene costs more relative to other uses of kerosene since those applications can tolerate kerosene of lower quality than aircraft-grade kero.
Those are for military use, where speed matters but money is basically unlimited.