In the cases of both the
Druze and the
Yazidis their refusal to spread/proselytize their faiths were adaptations to Islamic societies that would have destroyed them long ago if they had attempted to spread their faiths.
Similarly, secret societies are often secret either for safety, as in the cases of the
Carbonari or the
Sons of Liberty, to maintain power, as in the cases of many different secret police organizations, or as a means to be glamourous and recruit outsiders, many American fraternal organizations. These groups were secret for serious pragmatic reasons that either served to spread their memes or protected the existence of their memes.
Memes restrict their spread only to ensure their survival.