Notice how there is not separate rail for the upper rack. It sits on the props in the corners of the lower rack. You had two options: lift the upper rack out entirely, load the lower rack and then replace and load the upper rack OR lift out the center of the upper rack and load the lower rack through the rectangular opening which was like the older GE top load built-ins. I have looked at these machines in old houses at estate sales late on Friday afternoons when they are not crowded.
Also, notice the hardware cloth guard under the lower rack to protect the impeller.