Python 3 support graph for 360 most popular Python packages!
This site shows Python 3 support for 360 most downloaded packages on PyPI
There can be many reasons a package is still not supporting Python 3.
If you are package maintainer, it's time to start porting (if you haven't already). Here is an in-depth guide Porting to Python 3 and the official porting HOWTO. If you are not able to give the time needed, please seek for help from the community by announcing your need for help on blog, IRC, mailing lists etc.
If you are user of the package, send a friendly note to the package maintainer. Or fork it, and send a pull request to help move the project towards Python 3 support.
This site utilizes a little tool, caniusepython3 created by Brett Cannon. Throw your requirements.txt file at it and it will tell you which packages support Python 3, and list out which don't.