From what I've heard it was disabled because people's cars would be mint condition in their eyes but destroyed in other people's eyes, but cars are still like that even though it's impossible to cosmetically dent or damage your own car, it will still look destroyed and dented/bent out of shape to other people anyways.
Personally I find it really weird to get in a crash and my car looks perfectly fine, the deformation is an important part of immersion and additionally there is more motivation to not crash because it actually messes up your car, not only internally. I'm not sure how many would agree, but I find something is missing without deformation, I find it's a pretty big part of cars in games in general and it feels weird without it.
This has been done. Only a slight amount as anymore tends to look bad on some cars.