Usually, you would like your class to include the basic methods and attributes without knowing who is going to use it. A class Car shouldn't be aware of the application logic; thus there is no need to know that you need a List of Cars. Moreover, imagine that you need to reuse this class for another application that requires either a Map of Cars or another Collection of Cars, why to carry this unwanted List?
In your case I would divide the application logic from the class logic and create the List in a separate Class that indeed requires it.