why did the gulenists use bylock when they could have used whatsapp or signal? it looks like they are getting rounded up because their use of an obscure app has

why did the gulenists use bylock when they could have used whatsapp or signal? it looks like they are getting rounded up because their use of an obscure app has become a strong signal that they are gulenists. though, signal might have had similar problems. not sure how popular it is in turkey.