They also changed the C interface at the same time -- and many Python libraries had non-trivial amounts of C code in them because Python was and is so slow.
It was also for a time impossible (or close to impossible) to run the same Python code in 2.x and 3.x. It helped when later 2.x versions acquired more 'from __future__ import'.
They really aimed for making it maximally hard to support v2 and v3 at the same time which created a nasty coordination problem: why upgrade if the libraries aren't ready and why upgrade the libraries if there are no users.
It was also for a time impossible (or close to impossible) to run the same Python code in 2.x and 3.x. It helped when later 2.x versions acquired more 'from __future__ import'.
They really aimed for making it maximally hard to support v2 and v3 at the same time which created a nasty coordination problem: why upgrade if the libraries aren't ready and why upgrade the libraries if there are no users.