Requirements Uncertainty Anti-Pattern

One strategy I have seen for 'managing' requirements uncertainty is to hire permanent or contract developers so that they are available to respond to requirements changes. I call this the 'embrace and extend' anti-pattern. Instead of minimizing the chances of this risk materializing, or limiting the effect of this risk in the event it does materialize, this approach accepts the maximum penalty for risk materialization from the outset, and actually encourages requirements changes. Why do managers engage in this anti-pattern? What are some alternatives?