Why is it easier to walk on soft sand if we have flat shoes rather than shoes with sharp heels (or pencil heels)?

A flat shoe has a greater area in contact with the soft sand and exerts less pressure on the soft ground. Due to this the 'flat' shoes do not sink much in soft sand and it is easy to walk on it. On the other hand, a sharp heel has a small area in contact with the soft sand and exerts a greater pressure on the sand. Due to this, the sharp heels sink deep into soft sand making it difficult for the wearer to walk on it.