Why Isn’t The Entire Plane Made By The Same Material, When The Black Box Remains Undamaged During A Plane Crash?
This is one of the oldest jokes in aviation. But seriously the construction of the Digital Flight Data Recorder and Cockpit Voice Recorder boxes is amazing. A fair amount of their strength comes from the fact that they are filled with a protective material to shield the electronics inside.
For an aircraft to be built that way there would be no room for passengers.
In any case, as counter-intuitive as it might seem, you don’t want an aircraft to be too strong. The gradual collapsing of the aircraft structure absorbs some of the energy of impact (much like the crumple zones in a car) which means that the people inside decelerate at a lower rate. If the plane was too strong, it would stop and the people would keep on moving and that would be bad.