But until signal actually produced a usable (to the average person) app, people will continue to use telegram and other insecure chat platforms.
One "secure" approach would be that of the older Skype clients, where chat history synced between the logged in clients of a user. However, that was a horrible user experience, made worse by bad notification management.
So while Signal can get better, you will probably always have to decide between usability and security, which is most likely the very reason that "normal" people always end up with the less secure solution, which in turn renders the secure solution even less usable with its smaller userbase.
Also, I tried Wire recently, which has e2e and all your messages on all your devices. I tnink sent messages duplicated, encrypted with each of your devices keys. So when you add a device it can't read previous messages.
I am on Telegram primarily because it's the best I can come up with that my friends use, and moving my friends is an unlikely task as they have their friends on Telegram as well. You need to move or duplicate users from existing platforms to get a userbase, but you need a userbase to attract users from existing platforms.
I have been looking at Wire. They're using the signal protocol, but in a more closed model IIRC. I didn't know that they had a solution to this problem, though, and always just through of them as basic Signal clone. I guess I'll have to have a look. :)
Most users don't care about security and this should not be a problem.
Telegram is a very nice mobile platform. I use it to share a microblog (Telegram Channel) with some friends and it is very nice.
The only gripe I have with it is their propaganda on security.
Telegram is not secure, but I don't care, I already have Signal for sending encrypted messages.
I would say that it is a massive problem that users don't care about security, though. They just don't know, because they haven't been screwed over yet. People cared a lot in retrospect when the password bruteforce leaked iCloud pictures, for example. People don't care about politics before it's too late, either.
On a positive note, Facebook seems to be screwing itself over in usability and content. I used to be on there reluctantly, but now I only check the input every two weeks or so to check for annoying relatives that might message me. The news feeds are nothing but uninteresting clickbaits, and they keep making it harder and hard to just check the bloody messenger inbox.