I try to get all my friends to use it. Since a lot like to use WhatsApp anyway it usually isn't too hard. But Signal doesn't have a push from a big company like WA does. Generally it is my friends from India that I can't move, because all of their communication is done with WA anyway. But it doesn't seem unreasonable to me that such a stronghold could happen for Signal too. But it needs to be spread by word of mouth.

I don’t trust them to implement the protocol without deviating from the accepted safe practices surrounding them. It is against their interest.