While a high wing is great for a military airlifter because of the operating environment, frequently to less than ideal fields, it has significant disadvantages.
- Additional weight because you have to transfer loads a much longer distance between the wing box/spars and the landing gear.
- Wing box sticks through the cabin in an awkward position, cutting into useable space.
This pretty much explains why Boeing took their C-5 competitor work and used it for a clean sheet 747 design instead of modifying the aircraft into an airliner. None of the 747 proposals were high winged, though one was mid winged.
