The Bender tool you're using is doing what it's supposed to. But there's another tool called Bend that does more what you want. First select your object you want to bend. Then click the Bend tool and select the profile polyline you want to bend your object along. Sounds easy enough, but there is a catch. You have to be viewing your profile polyline from an angle that best shows the bends in it. In your case, the viewing angle is fine. If your camera was looking down at the profile polyline, the line would appear straight and so no bending would occur.

www.youtube.com/user/ShawnDriscollCG