It was released in 2008, about 4 years ago. And still programmers cannot fully switch to 3000 because it lacks so many libraries. I often read complains about how one cannot switch to 3000 because he uses some libs of v2 and they are not in 3000 yet and noone knows when they will be there. Pymysql is available only for *nix but not Windows and that is very commonly used thing - working with databases. Everytime I think about writing some app for people it works this way: I code it in Linux and then they use it in Windows. And because of this it cannot happen. I am always forced to go back to Python 2. But Python 3 is so much better as a language than P2. After digging into P3 I don't even want to deal with P2 any more.

You can find infos on this page.
Since libraries are often third party's it's difficult to answer but it's easy to figure out that most of developers are still tied to Python 2.x and don't want to or cannot improve their skills.

Here's what amounts to an official answer:

http://programmers.stackexchange.com/a/63935/16764

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The politically incorrect answer is: because Python developers care about production much less that Perl ones.

The transition from Perl 4 to Perl 5 was pretty smooth. I once read on Slashdot that Perl developers have a vast regression test suite ("smoke tests" IIRC), and that each Perl release is validated by the suite in order not to break existing code. The same post claimed that in Python world breakages are quite often.

And the Perl 5 to 6 transition might be finished after we're all dead.

Python 3 isn't intended to be backward compatible. Yes, this is a factor.

That is correct. But from the getgo Perl 6 wasn't meant to be backward compatible with Perl 5. OTOH. as I'm checking Perl 6 status, I see the Perl 5 compatibility layer growing wider/thicker.

I don't count on Perl 6; Perl 5 is far from dead, and new modules with nice language features appear. For example, I recently discovered Package::Generator, Sub::Exporter.

Still, Python 2 -> Python 3 transition is like Perl 4 -> Perl 5 transition. I.e. Python 3 finally caught up with Perl (I mean https://en.wikipedia.org/wiki/Closur...nce%29#Example - closures were introduced in Perl 5).