Making guesses here, it is most likely caused by tribes isolating themselves from others, reason for that might be a vendetta between families, which has a declining influence here in Turkey yet still a problem, or Shia communities in Sunni countries commonly marry their cousins again because of an isolation process and oppression faced in public. As performing their rituals outside of public eyes is quite common for Alevis.
Rest? I would say simply traditionalism and privacy understanding.
