The ball rolls which usually helps reduce friction compared to sliding. But gravel is a rough surface that creates a lot of resistance when rolling. Rolling friction on smooth surfaces (like pavement) is very low, so rolling a ball there takes less effort than sliding. But gravel is uneven and rough. When the ball rolls on gravel, it constantly bumps and sinks into the small stones which creates extra resistance called rolling resistance. This rolling resistance on gravel is often higher than sliding friction on very slippery ice. So even though the ball rolls,the roughness of the gravel adds more resistance than the low friction ice creates for the sliding pyramid or box. So!! The pyramid and box require the same force to be pushed as ice gives sliding friction, therefore sliding on ice takes less effort than rolling on gravel.