In the wild snakes can go to whatever area makes them feel most comfortable. In captivity they don't have that choice to find a new home if they don't feel safe in their current one, that's why people try to make the enclosure makes them feel as secure as possible. A smaller enclosure will do that for a younger snakes because they feel less exposed. A bigger enclosure could also be set up properly to make them feel comfortable, but if done improperly it can easily stress them out.
Thats what hides and shrubbery are for.
but I see your point. I still do keep my younger snake in smaller enclosures because of this.
Although I do believe they can be successfully kept in a large enclosure if enough hiding areas are provided.