Like others said, I think it depends what the crash has done to your car underneath the body panels as to whether it is worth keeping.
The repair/body shops that these insurance companies use charge a fortune to do the work, so even if you have a very small scrape, they factor in the cost of the vehicle/age etc and then the cost the repair/body shops charge and go by that.
Sometimes it is best to just get the car back from the insurer and source the parts yourself and take it to some other good repair/body shop of your choosing if you really want to keep the car. In fact most of the time, the very same repair/body shops will do the work for half of what they originally would have charge doing it through your insurance. That might be worth doing if the car is special to you, but remember it will always be tagged as written off in your documents.