Crazy Canards! but as Daffy Duck would say, " that's deshpicable"I think privacy is one of the main keys to getting them to lay in their nest boxes. They need to be dark and hidden.
Also, since I let my ducks out early in the morning, they haven't always laid their eggs by then, so I scatter boxes around their yard as well. It seems to work better to have boxes scattered here and there, rather than a neat row of them.
And they pay more attention to new nesting locations, so sometimes I even move the boxes. Recently I moved one under a cluster of thorny bushes, and put a cinder block in front of it to make it even more private. Almost immediately, about five ducks decided they wanted to lay in it. A few weeks later, no one cared anymore. So I moved it again. And they laid in it again.