The big issue for you, perhaps - but the reality is that most users simply don't care about that.

Most users don't care because there is no way and they're not technically minded enough to complain about it. They would use it if available. I can cite many examples of non-technical users who had conversations like "do you have whatsapp", "do you have viber", "do you have X". From that it's safe to say there's a need for interoperability, and to be honest, if messengers get more important, some regulatory body will force it like they did with other things in the past.