Nature shows us how to build things that last, if we pay attention. Your find with creek banks and your concrete mix is spot on. How many other fixes are we missing by not copying what already works?
Hold on, is it really that big of a miss? Sure, tree roots are cool, but we also need stuff built fast and cheap. Like @knight.uma said, we overcomplicate things, but sometimes the simple, natural fix isn't strong enough for a highway or a big building. We probably copy more than we realize, just not for everything.