I'm not sure if the watchtower conforms to any known business model. It is unique in that it trades on hope, faith, world events, and mortality. It claims to have divine insight into the world of mankind. Disasters and disappointment/disenchantment with society play into its hands and in effect increase its market value. Personal awakening and a resolve to overcome the pain threshold of leaving, is one way it may lose its shareholders, the congregations.But that too, brings with it the pain of writing off years , sometimes many years, of financial and emotional investment.
The meetings and literature etc feed on fear and mortality, constantly reminding the shareholders that they are answerable to the chairman, God. Conventions and assemblies mimic shareholder meetings, and cynically congratulate or excuse a good or a poor years trading. At the same time, shareholders are encouraged to view investments over the longterm, and remain faithful, or loyal, to the company and it's perceived chairman.
It would be nice if some did leave en masse, as it could be just enough to encourage others to follow suit. However, as a charity, it is propped up with tax privileges and so remains seemingly financially invincible, unless a totally unseen financial hit occurs, or govts withdraw tax benefits. Donations from individuals strengthen their loyalty (or speculation) as they seek a final dividend sometime in the future...