Modern CPUs have many cores. Some parts of blockchain applications parallelize perfectly (like checking digital signatures) while some parts don't parallelize at all (like executing transactions in order). Modern C++ has a very good mix of effective inter-thread communication and optimization of single-thread performance.

C++ doesn't have a run time that stops the world or manages memory, giving your application consistent control over this behavior. Move semantics allow you to get objects that behave like values (i=j; a+=1; does not change j) but perform like references (deep copies are avoided except where needed).