The short and simple answer is because it is substantially faster (and has a hugely less memory overhead). It is easy enough to modify the c-python source to try this.

Why it is faster is the article helps cover... some of the tricks for optimizing small object allocation and reuse that c-python performs are not done by the c allocator. As to why THAT is, I can only appeal to your intuition that not all applications allocate memory in the same way so an allocator optimized for Python's behavior has an advantage.