Well, if you don't put some tubing through the frame, you will smash it when you tighten the mounting bolts. You don't want your frame smashed flat. The steel is actually really thin and weak. Any frame mounted steering box puts a good amount of stress on the frame especially when turning the wheels while sitting still or up against a rock etc. The reason for the cross member is fo that you don't get any flexibility in that section of the frame. Even just a few millimeters of frame flex can make it drive like crap on the road and make it impossible to align. If the frame does have some flexibility to it, eventually the metal will become fatigued in those areas and cracks will form. A cracked frame is not good either.