It doesn't really matter. A secret society should be harder to maintain than a public guild. Even a public guild requires an aspirant to find a guildhouse. Why should a secret society be any different. But on top of that, one can't simply waltz into the Dark Brotherhood of Shadows. No, he needs to meet one of the Dark Brothers who will lead him in. If those who run the society can't or won't put in the effort and the thought into getting new members in ways that don't draw unwanted attention then that secret society doesn't exactly deserve to be a secret. Or exist.
