If you look, the anti-climber is still commonly used on locomotives, though I can't speak for transit designs or how effective they are with Jim Speaker. :-)

Even with various coupler designs that also work to prevent vertial separation, at some point a collision becomes so violent that it doesn't matter - especially when the incident has exceeded the design capacity of the coupler shank and it breaks.

There are two thoughts (and resulting government edicts) of accidents - one is to make the equipment provide protection for the occupants to survive the accident (requiring heavier equipment - therefor increasing the mass you need to be protected from) - or to prevent the accident in the first place. Unfortunately, niether is entirely fool proof. The odds and rules of physics catch up sooner or later.