Because you can't just strap a nuke to a pylon, pull the safety pin from the fuze and fly off into the sunset in your cowboy hat. You need an extensive set of

Because you can't just strap a nuke to a pylon, pull the safety pin from the fuze and fly off into the sunset in your cowboy hat. You need an extensive set of avionics to control and arm the nuke in the plane which add substantial cost and aren't designed for/integrated into all aircraft.