Many useful libs still aren't ported and some likely never will be (like Twisted). But more importantly, there is a vast amount of application code out there no

Many useful libs still aren't ported and some likely never will be (like Twisted). But more importantly, there is a vast amount of application code out there not ported. If you're working on a py2 project it's even hard to start new projects with py3, since you get no interoperation. Breaking compatibility should have never been done without being able to run both py2 and py3 code in the same process.