In addition to the other reply, there's often a reluctance -- on the part of both the Python core team and the developers of popular third-party code -- to add things to the standard library, since doing so ties you to Python's development process and release cycle. This is one reason why pip is not in the standard library, for example (instead, Python ships a module which will go get pip for you); it needs the ability to develop and release at its own pace and on its own terms.
