I think part of the problem is that there is no infrastructure for something like this on iOS and Android.
With webOS, there was a single messaging app that integrated SMS, Skype, Facebook and Google. The latter part was implemented using libpurple, so it was relatively easy to extend this to all messaging that libpurple supports.
I really liked that approach (marketing name was "Synergy", unified messaging was only a small part of this), but it's quite obvious that neither Apple nor Google have any interest in adopting this unified approach for anything but their respective own messaging of the day.
I think if we could get the world unified on a single chat protocol we can expect things like this to emerge. Of course it will be unlikely to happen soon, if at all.
Plus we all know that Google really wants to own a chat app so maybe they will decide not to make it first-class in Android i fit seems like a threat.
A few years ago I was in contact with someone from the project to integrate the changes that I did, so their messaging client should now support pretty much everything that Pidgin supports (which, as I learned today, nowadays includes Matrix, Signal, Telegram and Steam as well through plugins).
Maybe I should install that on my old Nexus 4 and see how far they got... :)
With webOS, there was a single messaging app that integrated SMS, Skype, Facebook and Google. The latter part was implemented using libpurple, so it was relatively easy to extend this to all messaging that libpurple supports.
I really liked that approach (marketing name was "Synergy", unified messaging was only a small part of this), but it's quite obvious that neither Apple nor Google have any interest in adopting this unified approach for anything but their respective own messaging of the day.