Back car bumper

The plastic bumper cover is cosmetic, not structural. I am pretty sure there are products to repair them, but body shops make the most money when they save you money in the long run, so they will replace the entire cover and paint it. Repairing a damaged one requires removal and reinstalling too, plus repairing and repainting it. When you are paying almost $100.00 per hour for labor, you want the repair that takes the least amount of time. New parts often cost less than the labor dollars to repair old ones.

Yep. You might actually find nothing but a huge chunk of Styrofoam behind it. That is there to hold the shape of the cover. It is supposed to absorb part of a crash impact. If this were a steel bumper, the strength of it would have transmitted the force to the trunk floor and rear quarter panels. Possibly the rear windows would have shattered too. While this can be disheartening, it would have been much more expensive on an older car.

You may be a little surprised when you actually take that bumper off. I worked at a shop that also did this type of work and quite often you find a lot more damage than expected behind that bumper. There are reinforcements and body panels that often get bent.
Auto body labor rates are much lower than mechanical rates and more commonly found around the $50 per hour range. What is the highest cost by far are the refinishing materials. Shockingly it is not unusual to pay $300 in refinish materials to paint a $150 bumper.