Legacy doesn't mean unused, the definition of a legacy programming language is when no one is choosing it for new projects.
Python2 is going to be moving closer to this COBOL-status as people start coding for Python3 and Py2 support becomes more and more of an afterthought until they just stop bothering.
Even if that were true, which I would disagree that anyone writing a library from scratch today is ignoring Python3- over time it is an inevitability once the core dev team drops support for 2.7