Rather, it's a side effect of needing large amounts of computational power for our highly refined motor skills.
Many lower animals (with lots less "computational power") are capable of feats that require excellent motor control. They don't necessarily qualify as "intelligent" in the human sense. And the motor control cortex of the human brain is only a small part of the total structure.
"it is comparatively easy to make computers exhibit adult level performance on intelligence tests or playing checkers, and difficult or impossible to give them the skills of a one-year-old when it comes to perception and mobility."
Because you can't work on a solution if you don't understand the problem. You can't code what you can't codify. Much of what we are able to do depends o unconscious knowledge that's difficult to codify (since we do not consciously execute an algorithm).
Polanyi: We know more than we can tell
http://infed.org/mobi/michael-polanyi-and-tacit-knowledge/
Which has lately been called a paradox:
http://philosophicaldisquisitions.blogspot.com/2015/10/polanyis-paradox-will-humans-maintain.html