The main problem is that everyone wants to profit from messaging in some way (carriers, google etc.) whereas there is only nominal cost to run messaging (not including development hours). Whatsapp was able to do it with $1/year. So there is no way to break this conundrum in the standard capitalistic model. If they were looking for technical solutions, they could have implemented something like signal as an AOSP app and be done with it. But there's no money in that.