Django's lack of Python 3 support is big reason Python 3 adoption is slow, at least in the web dev faction of Python's community.
Why get comfy with Python 3 when you must remain attuned to the conventions and quirks of 2.x in order to use Python's most popular web framework? Folks keep talking about Python 3 because they really want to use it, but have reservations about adopting 3 when 3 isn't supported by useful frameworks.
Once Django supports Python 3, that reservation vanishes. Python 3 will be adopted by more people and get support from more frameworks.
tl:dr; Django's popularity holds dev community captive to Python 2.x, slows adoption of Python 3. Django team announces Python 3 support not in distant future but near future. Folks get excited. "About damn time."