Why commercial airliners cannot become COD aircraft

Why were airliners such as the 727, 737, F28, and DC-9 unsuitable for carrier onboard delivery?

Their structures, size, and cargo arrangements were built for land operations, while catapult launches and arrested landings impose severe rapid loads.

Carrier aircraft experience abrupt acceleration during launch and even harsher deceleration when an arresting wire stops them. A large airliner's fuselage and wings respond differently to those rapid changes in load, placing exceptional stress on the structure. Passenger layouts also make poor frontline cargo aircraft, and several candidates would struggle to fit or move around a carrier deck. Engineers may still study such airframes to document why an apparently cheap proposal fails. The He 177's dive-bombing requirement illustrates a similar mismatch between a large airframe and the loads demanded of it. A viable COD aircraft needs a structure designed for carrier loads from the outset, perhaps enlarged carefully after that foundation is proven.