I am not sure about now, but another point is that when Python 3 was released it was slower as well, so there was hardly a reason to swap for very minor changes and no libraries. Python 3 should have been something radical like PyPy or large changes to the standard library.
There were large changes to the standard library :). The big io rewrite, for example (which was also one of the reasons for the slowdown initially as it was implemented in pure Python; it eventually got rewritten in C and should be faster than before now).
Anyway, I think it makes more sense to major-version language than implementation changes. In theory CPython vs. PyPy shouldn't matter to code.
