Well, there are attempts to this, e.g. Matrix. They even show cases how you can open up an existing closed messenger: https://matrix.org/blog/2020/12/07/gitter-

Well, there are attempts to this, e.g. Matrix. They even show cases how you can open up an existing closed messenger: https://matrix.org/blog/2020/12/07/gitter-now-speaks-matrix https://matrix.org/blog/2020/12/07/gitter-now-speaks-matrix However, existing tech giants have little reason to do so, unless users vote with their usage (which is sabotaged by lock-in effects through the existing social networks...)