Everyone has time and ability to make their own choices with like-minded friends. They do it for everything else, that's how they started using WhatsApp and co in the first place. Their claims to caring about privacy are as convincing as a friend who keeps telling you "sorry, I'm too busy", "another time then?", "maybe", repeated ad nauseam. Then you see them at another party with someone else confusingly named "WhatsApp" and you realize they just couldn't make time for you, who is named "Signal".
Again, look at how quickly users switch when a service requires payment (IIRC WhatsApp did try to do this once and a lot of users chose to leave instead of paying). They're just too busy & helpless, right? How much proselytization did that take?
This was a process, not a 1-day switch from skype to whatsapp. The network effects are real, and if you don't understand how difficult it is to get people to join a chat app, you won't win.
Of course it's difficult to get people to join a chat app, and it should be. At a minimum you should need to provide something that users want and didn't have before. WhatsApp offered something new, it was an effective price tag of zero with phone number contacts. Skype offered something new and desirable (until it didn't). Snapchat offered something new and desirable. All of them had predecessors with network effects and still succeeded by giving users something they really wanted. They didn't throw their hands up and blame users.
Surprisingly though, Signal is gaining a bit of traction, so I think "Privacy" is still something people do want. But it has to be better defined.
And to be completely honest I don't believe in Signal. The current messenger wars kind of feel like a parallel universe's email wars "yahoo vs gmail vs hotmail vs live" or something. Coming up with a new messenger is easy. Most of them have the same featuresets. The underlying protocols should be compatible instead of this sorry state of affairs.
Matrix will probably win out in the end but it's going to be long-drawn and unnecessarily annoying for users in the mean time. It shouldn't matter if you're using instagram's UI, or messenger's, or signal's, …. You should get access to the contacts you want, and be able to cross-talk.