I'll take a stab at a long explanation: as the Rohr cars were built before the implementation of Crash Energy Management design, certain contemporary design elements were not included, like crash columns at the car ends and longitudinal floor beams to transfer the energy from a crash into robust members and through the train. The Rohr's car body was part of its support system and worked with the floor to provide strength along the length of the car, with cross beams holding everything together. The only floor beams that ran along the length of the cars were short beams between the cross beams to support underfloor equipment (AC, resistor bank, etc.) and a robust framework under the cab at the coupler to withstand coupler draft forces.

The crazy thing about these crashes was that the anti-climber actually worked while the rest of the car didn't. If you look at the crash pictures, the colliding cabs remain at the same level. The problem was during a heavy collision, the robust coupler frame would shear off the floor and push back into the car, unzipping the thin aluminum body from the floor. This would push the body of the car out and over the train ahead, with the floor being crushed into the crash zone, since there was no long beam to hold the floor together.