It's not hidden. It's just not connected to an internet-style social network. Interest can still spread through word-of-mouth, even if the platform doesn't provide any tools for audience measurement and management. It's akin to a 'zine from the pre-internet days, except it doesn't cost as much money to distribute.

EDIT: A 'zine isn't a perfect analogy, since someone who published it would know how many they printed. A freely copyable newsletter would probably be a stronger analog.