The game is not multi-core/thread optimized at all. The whole game runs almost completely on only one core...
That is how well most games (and programs generally) work. Only a few specific tasks benefit from massively parallel processing and while most other can benefit from some parallelisation, gains tend to be smaller due to resource conflicts.
Developers should focus on getting code right, fixing bugs and dealing with compatibility issues - performance and multi-core usage should be left till later.
