Consider the fact that a horse walks on what would be your “middle finger”. Why do you think that bone is so much larger and so much more developed in a horse rather than humans?

To support the high body weight.

Explanation:

The bone of feet is much larger and more developed in a horse rather than humans because this large bone helps the horse in running and provides support to the leg to bears body weight. The horse weight is so much high as compared to humans so it needs more strong bone in finger of his foot. The more development of the bone also occurs due to the function it performs so that's why the bone is more larger and more developed in a horse than humans.