So imagine the horizontal distance, not the diagonal distance.

The front foot is the equivalent of the top of a river up a mountain, and the back foot is the equivalent of the estuary at sea level.

The human's horizontal foot distance is much less, so there is a much smaller difference between the potential from one foot to the other.

Imagine it more as water flowing downhill. Small horizontal distance, not too much change in gravitational potential energy, but from the top of a mountain to the bottom there's a huge difference there.