Hopefully this serves to be purely for education of plastic bumper covers or as known in the industry, Fascia.
Think of the term Fascia and that alone should tell you the intent of these covers. They are nothing more than the final cosmetic finish for the car. They are not there to protect you and I assure you, if that is all you had, you would die in an accident.
The following photo illustrates what happens when your wife slowly rolls to a stop, not hitting an object, just simply putting pressure on it. The result is a gauge in the material. Granted, this is hardly any damage but that is precisely the point. Hardly any damage from merely applying pressure to an object that in turn left a lasting impression.
This is quite common in cities like NY where there is parallel parking. Cars have license plates with screws to hold them protruding. As folks try to leave tight parking spaces, they bang into the cars in front. While not causing major damage, these lasting impressions in the material occur.
Here is the area that she stopped that I have now removed the offender.
So, that all said, again, now imagine what would result to molded plastic when it is compressed with great force up against steel? What exactly can't be predicted in detail but we know one thing for sure, it would be significantly greater than what is on that neighbor's car.
Hope this comparison assisted.