Problem is, they only have two limbs to do this with, unlike all the other modern anthropoid apes, which have four. This is because we've had to adapt one set of limbs for walking upright. For that, we need a rigid foot with an arch to transmit the force our leg muscles are applying from our ankles to our toes, and especially our big toe, so that, as our body moves forward we push on the ground with our toes and so keep the momentum going.
|Australopithicus afarensis (Lucy)|
But what about those muscles which were once used to grip with the feet? Well, one of the more important ones was the plantaris muscle. It's still there but serves no purpose at all. In fact, 7-10% of us are born without them and suffer no ill effects or disadvantage at all. It is regarded as disposable and is sometimes removed by plastic surgeons to be used in reconstructive surgery elsewhere.
It is merely a vestige; yet another fossil from our past when we could get a grip with four hands instead of two. No intelligent designer would include something useless that its design can do without. The human plantaris muscle, like all the redundant structures which abound in nature, is the work of an unintelligent designer without a plan and a process which is slowly eliminating it, with no particular hurry because it doesn't do any harm either. This is one of the ways in which we know the human foot evolved and was never intelligently designed.
What does it mean to be human? (Smithsonian National Museum of Natural History)
Evidence for Human Evolution.