R is a funny language because there are a lot of things in it that are just objectively bad, yet I still love it. Probably because of the community and CRAN. Of course, R is really just some syntax wrapped over C++, and it is very extendable using C and C++ when needed, so I don't think you can really say, in absolute, that R doesn't scale. Someone has written a package to scale whatever problem in R, you just need to find it.