"How rich do you have to be? Who decides? And how do you keep a secret like that?"
That's the whole point of secret societies. They haze you to see if you're down with the program before they let you in. All discussions of "they could synthesize it" or "they could get rich off it" are beside the point. The culture that does this already exists and has for millenia and has a way of doing business that they're comfortable with and kills anyone who intrudes. They have no interest in trying another approach. It's a cartel. Go watch a few vampire movies, which are metaphors for all this stuff. You'll see a recurring theme that sure there are other ways for vampires to get what they want but they're not interested because this is how they've always done it and they enjoy being vampires, like to keep it exclusive, and like hating on non-vampires. You tell a vampire he could get rich by selling synthoblood to normies to make them immortal like himself, he'd say thanks but no thanks. The movie "Daywalkers" is about exactly this.