Values, character attributes, and growth define civilizations and the people within the society. These are the core of why people function with their laws, and why they may see fit to fight against those laws. Classic characters have cores that are trying to be understood. The authors of these classics may be trying to show people that there is a piece of this core that is missing within the society they currently reside. Some great examples come from The Swiss Family Robinson, Iliad, Beowulf, and others like those listed. In each of these books, we see people discover for themselves, through study or adventure, what is lacking in their life to allow them to be better.
The lack of good examples, in individual lives means that the classics are one of the few resources for people to learn morals and principles.