Why do people hesitate to use Python 3?

Question

Python 3 was released in December 2008. A lot of time has passed since then but still today many developers hesitate to use Python 3. Even popular frameworks like Django are not compatible with Python 3 yet but still rely on Python 2.

Sure, Python 3 has some incompatibilities with Python 2 and some people need to rely on backwards-compatibility. But hasn't Python 3 been around long enough now for most projects to switch or start with Python 3?

Having two competing versions has so many drawbacks; two branches need to be maintained, confusion for learners and so on. So why is there so much hesitation throughout the Python community about switching to Python 3?