Racecars are a weird animal. To race teams, they are just tools. Even if they win, as the regulations and stuff change they either modify them to keep them relevant, or they just kind of get tossed a lot of the time when they are no longer viable or competitive. I think fans care more about the history of the car than the teams a lot of times.
That's not to say that we shouldn't preserve them to some degree. On the other hand, a lot of those cars are made up of custom parts anyway, and someone was able to make them in the past, so someone is going to be able to make them again today. I wonder how many of those cars are more like a ship of Theseus today. A team isn't going to go out and win Le Mans, then mothball a car and say "cool, that was fun". They are going to keep racing it in the series. So even if a chassis might have accomplished some impressive feat, I have a feeling a fair amount of parts on the car by the time it enters private ownership are likely not the ones that were on it when it won whatever race.