The structure between the wings is one of strongest parts are the aircraft. With low-mounted wings, the fuselage sits on top of that structure and only needs to

The structure between the wings is one of strongest parts are the aircraft. With low-mounted wings, the fuselage sits on top of that structure and only needs to support its own structure. The wings are pushing the plane up. High-mounted wings, on the other hand, pull the plane up. This requires the fuselage to be stronger. Otherwise the wings would rip off the top of it.