How can nested convention plugins set up in Gradle?

I am trying to set up nested convention plugins in Gradle. This is what I have written so far: https://github.com/gradle-templates/gradle-conventions-plugins-template. This is not working as expected and the nested plugins are not detected. I am not sure what I have missed here.

So how do you write nested convention plugins in Gradle? I am trying to have each convention plugins as a self-contained project included as an included build.