In some environments, wheels are simply not as good as limbs for getting around. So it may be that, even if it were possible for wheels to evolve, they would not be found often in nature. In fact, given the limits of wheels, the main question can be turned around: instead of asking ""Why doesn't nature use wheels?"", the question becomes ""Why don't people build more machines with limbs?"" In engineering, wheels are often used instead of limbs, because limbs are more complex to design and control—not because wheels necessarily do the job better.