Why ship-scale steam favors boilers

Why did ships use steam boilers rather than the compact generators demonstrated in steam cars?

The fuel and efficiency tradeoffs change at ship scale, where conventional boilers make more sense than systems optimized for cars.

A steam car and a large ship ask the plant to deliver power at radically different scales and duty cycles. Fuel choice and overall efficiency are where the comparison breaks down. A device that performs well in a car is not automatically the most practical machinery for sustained marine propulsion. Naval engineering choices have to be judged at the scale and operating profile of the ship.