Seized ball joints act like someone is holding the steering wheel while you are trying to drive. When you steer a little bit you encounter resistance, turn harder, overcome the resistance and overshoot your intended position. And, since the wheels can't self center on their own, you are constantly fighting to keep them on center. ( and overshooting )

I haven't driven a street bike but it would be the same as turning the steering damper all the way up and then some, riding around without leaning just steering.