Why didn't the official bittorrent client run on Red Hat Linux (w/o downgrading your Python) for at least three years? Why was NLTK stuck on Python 2.4 for yea

Why didn't the official bittorrent client run on Red Hat Linux (w/o downgrading your Python) for at least three years? Why was NLTK stuck on Python 2.4 for years? I might use Python to use NLTK, but why do I have to choose an old Python to get it to work... And what if I want to use it w/ software that needs Python 2.6?