He mentioned implementors of frameworks specifically, not users of frameworks which you seem to talk about. Julia is superior to R and Python as a language for package development. This is illustrated by the fact that almost all big popular Python libraries are made in complicated C++. In Julia all the popular packages are native Julia, because it is a high performance language. It means it is much easier to get package contributors and feedback and help from package users. This is why Julia is moving forward so much faster than Python despite having much smaller mindshare.