Again, I'm not defending the insurance companies, but what you owe and what's it's worth are two different things and not their problem. The insurance companies don't "value" the car either, they use 3rd party data like NADA or Kelley's. When our van was totalled, my insurance company (granted, the other guy was at fault and my insurance would re-coup later) took the base value, added in the (optional) aluminum wheels, luggage rack, etc, etc to determine the final value. They also rated it in "good" condition (and I would have said fair, i.e. lower than good).
Look at a case where someone is upside-down in their car loan and then trade it in on another new car and go further upside-down. Let's say their $20k car has a $26k loan against it. If they totaled it the next day, you know how many people think "they (the ins co) should pay off the loan" ?? Lots do....