Why is only a small area in the sensory region of the cerebrum is sensitive to stimuli from the leg?

Question

Why is only a small area in the sensory region of the cerebrum is sensitive to stimuli from the leg?

Answer 1

Google the word, "humunculus" and it will reveal the spots on the cerebrum that handle the input from various regions of the body.

Your question is a lot like asking, "why does the motherboard on my computer have a circuit in one spot that handles specific information?"  Each part of the brain, like a computer, has a specific signal and function.

Answer 2

Because other areas are designated to the parts other than the leg.