Serious answer (seriously): because Python 3 didn't break enough stuff. For all the complaints, Python 3 was incredibly conservative about making changes that

Serious answer (seriously): because Python 3 didn't break enough stuff. For all the complaints, Python 3 was incredibly conservative about making changes that would completely break existing code. String handling was basically the big shift, and if you were writing good code to begin with wasn't super hard for most problem domains to adjust to. Clearing up some cruft in the way the standard library was organized wasn't hard to deal with either. And there wasn't a lot of new syntax in 3.0/3.1 and quite a bit of it was backported into 2.6/2.7 to make the transition easier. And then there was a bit of a moratorium on language changes in 3.x to give people time to catch up from their 2.x codebases. The result of which is a lot of people who didn't think Python 3 was a big enough deal to be worth putting in the effort to migrate, when the 3.x series started releasing. And now many of them are finally noticing all the cool stuff that's in 3.x now (3.6 is about to release), and noticing that their favorite tools and libraries have switched from "we support 2 and 3" to "we're dropping support for 2", and realizing they didn't take advantage of all the time they had to port stuff, and are angry and feeling left out and trying to find complaints to level at Python 3 in the hope that enough people will agree and just magically end it, port all the new features back to Python 2, and let them keep going as-is.