I don't know whats so hard for people to understand about this? This is a very valid point. Most, if not all, car COLLECTORS, not people that just buy a few cars, but real collectors (like Jay Leno) don't drive ANY of their cars. They keep the motors in them 100% with NO miles on them. They keep the value. If I buy a car today and keep it in a garage for 50 years, that car will have all original parts including motor and will be worth A LOT of money. Collectors aren't focused on accidents and theft when they chose to not drive them (as a few people mentioned) lol.
Back to topic. I think some people like to portray, what I said before, in the game. The game IS partly about collecting, isn't it? Why not keep your collection mint? You'll have something rare and could be worth a big trade for someone. I know its just a game, but, someone who can't afford to be a collector in real life, for obvious reasons, might choose to do so in the game. Its all about self satisfaction.
But again, this is a game. They're just numbers calculated by code. 0/0/0 cars are only rare and desirable because they've been made that way by the people that collect them.