With the weight you have on your hands being less than the weight born by the fork, then a smaller and weaker spring might be used. Less weight is bobbing up and down that on a fork shock, because there is typically 35%-40% of your weight on the front wheel but only a few pounds on your hands. Less mass bobbing up and down means you don't lose that efficiency. The physics/mechanic geeks let us down on this thread, not jumping all over that.

So why are there no hood covers with 2cm shocks built in?