Imagine the scene in a realistic mode; This soil gradually built up through distant impact / deposits and settled. The Rover is coming to a stop on soil that has been there for countless millions of years. The wheels gently passes over at less than 1km per hour to a stop and the astronauts depart to explore... shallow tracks.
1) Now the astronauts disturb the soil instead. This time they make an imprint, twist around to unload equipment, or to take a picture, pose for a picture and so on. The same soil is being disturbed over and over, becoming more dislodged upon each impact.
2) The tread of the boots is quite deep. So the load impact at each step is made not by the whole boot at all, but the parts that protrude only at first. Greater pressure is exerted onto the soil in a much more concentrated form until the entire boot sinks down and reaches the surface. Then the full load of the astronaut will be felt by the soil. The load from the rover is spread out by the flattened part of four wheels.
3) Plus the easiest method of getting around on foot sometimes is to hop. A greater load on impact could be greater than the Rover... a thud rather than a gentle roll.
Wouldn't the imprints of their boots now become deeper than the Rover's tracks for three reasons? The answer lies not just with weight distribution, but mainly with repeated disturbance. And that is it folks! No mystery!
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Some photographs show very shallow tracks made by the rover. The vehicle would have the weight of itself plus the two astronauts. And yet beside the rover, the astronauts footprints alone are deeper than those made by the Rover. How come eh?