First and foremost, I'm not raising this issue because I believe garbage collection is beneficial. 
My major reason for asking is because Bjarne Stroustrup has said that C++ would include a garbage collector at some point.
That being stated, why hasn't it been added? 
Garbage collectors for C++ are already available. 
Is this one of those "easier said than done" situations? 
Or is there another reason it hasn't been introduced (and won't be in C++11)?
To be clear, I understand why C++ didn't include a trash collector when it was initially designed. 
I'm curious why the collector isn't included.