The summary: "First, git's Windows support is the weakest out of the three DVCSs being considered which is unacceptable as Python needs to support development on any platform it runs on. Since Python runs on Windows and some people do develop on the platform it needs solid support. And while git's support is improving, as of this moment it is the weakest by a large enough margin to warrant considering it a problem.<p>Second, and just as important as the first issue, is that the Python core developers liked git the least out of the three DVCS options by a wide margin."<p>I'm using Mercurial for the same reason - Windows support without complex dependencies.
There is a lighting talk of some of the reasons at PyCon 2009. <a href="http://pycon.blip.tv/file/1947231/" rel="nofollow">http://pycon.blip.tv/file/1947231/</a><p>The talk starts at 3:45.
I think they mainly chose it because it's what the community wanted. Git is very popular with Rubyists, and Pythonistas like to be a bit different than Rubyists. Instead, they chose hg, which is essentially git, with different names for things. Hg is a perfect fit for Python, as thats about how different Python is from Ruby or vice-versa ;)