It has to do with the orientation of the model in gmax, Blender or whatever it was made in. If the creator made it 'sideways' then I doubt you can do anything about it.
Another problem is that the object's default origin (the 0,0,0 point in gmax etc) may not be in the physical centre of the model (eg. the creator may have made the mesh to one side of the origin for some silly reason). In that case it won't sit in the middle of a flatcar, but closer to one end or one side. Again, short of getting hold of the original gmax files, there would be little if anything a user could do to fix it.