I'm pretty sure the world doesn't use it more because it doesn't have a flashy marketing campaign and trendy developer tools/libraries don't have a plugin for it. If a whole bunch of developers aren't writing blog posts about it, does it even exist? Plus, it's old, so it's bad.
zmq was pretty dang trendy for a while. It had a well styled website and very wide language support. I think it just failed to deliver on its promise for most users.
