Ask r/ML: Why isn't R used often for game AI?

I'm an undergraduate student, learning R at school, and I've been lately exploring use cases for R, and taking a look at several of the packages on CRAN.

I've noticed that there's a lot of data mining/classification type packages, and a lot for specialized fields, like ape for bioinformatics, and many more for natural language processing. However, I haven't seen any for game decision trees, say chess or Go.

I guess that C++ is often used more, because every bit of speed matters and it's easier to write object-oriented code in C++, but I can't imagine why R wouldn't be a good contender either. Could anyone with experience in this area maybe explain why?