Some crash bars have an additional plastic block on crucial places. This adds to the effectiveness of the system, of course, but it is also a visible reminder that you have crashed your bike. And some memories are fun, but when it comes to damage, we prefer to make it go away asap.
If possible, you'd rather replace only a plastic slider block, instead of a much more costly crash bar.
To be clear: these are specific crash bar parts, for specific crash bars, on specific motorcycles.